NorthWestern Energy Group, Inc.

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 14A

Proxy Statement Pursuant to Section 14(a) of

the Securities Exchange Act of 1934 (Amendment No. )

NorthWestern Energy Group, Inc.

(Name of Registrant as Specified In Its Charter)

(Name of Person(s) Filing Proxy Statement, if other than the Registrant)

2026 ANNUAL MEETING OF SHAREHOLDERS

March 12, 2026

Strategic Merger: Building a Premier Regional Utility

If there were a single development that defined 2025, it would be our transformational agreement to combine with Black Hills Corporation in a merger of equals, announced in August.

This all‑stock, tax‑free transaction advances our strategy to build a stronger, more resilient regional utility with greater scale, diversification, and long‑term growth potential. The combined company will serve approximately 2.1 million electric and natural gas customers across eight contiguous states, with a market capitalization of approximately $9.8 billion and enterprise value of $18 billion. The merger is expected to be accretive to earnings per share in the first year and supports a higher long‑term EPS growth target of five percent to seven percent, with closing anticipated in 2026.

For shareholders, the benefits are compelling. Increased scale strengthens our credit profile and access to capital, enhances operational resilience, and expands our ability to pursue accretive growth opportunities. Just as important, NorthWestern Energy and Black Hills share a strong cultural alignment rooted in safety, operational excellence, customer service, and constructive regulatory relationships. Together, we will be better positioned to serve our customers and communities with excellence and deliver long‑term value.

Growth and Infrastructure Investments

Our strategy is supported by disciplined investment in infrastructure and ensuring adequate resources to serve our customers across our service territories.

A major milestone in 2025 was the acquisition of Energy West’s natural gas distribution system, adding approximately 33,000 natural gas customers and 43 skilled employees to our Montana operations and strengthening long‑term system reliability.

On January 1, 2026, NorthWestern Energy became the majority owner of Colstrip Units 3 and 4, increasing our ownership stake to 55 percent. Acquiring the interests of Puget Sound Energy and Avista at zero cost allows us to meet growing customer demand more affordably and reliably than constructing new generation resources.

In South Dakota, we are replacing an aging diesel‑fired plant near Aberdeen with two new natural gas turbines expected to serve customers this year, and we continue planning a new 131‑megawatt natural gas facility to support regional reliability.

Across our footprint, we plan to invest more than $3.2 billion in grid modernization for 2026 through 2030, strengthening transmission, distribution, and generation infrastructure while improving resiliency and system performance.

Looking Ahead

Operationally, our performance remains strong. In 2025, customers experienced 99.985 percent reliability, placing us in the top quartile of industry peers despite the challenges of an expansive, rural service territory.

We also made meaningful regulatory and legislative progress, including constructive rate settlements in Montana, Nebraska, and South Dakota, and passage of Montana House Bill 490, which provides important clarity around wildfire liability and supports continued investment in mitigation and grid hardening.

As we prepare to join forces with Black Hills Corporation, our focus remains on delivering value for shareholders, supporting our communities, and powering progress for the customers we serve. While our company will evolve, our commitment to our SERVICE values—safety, excellence, respect, value, integrity, community, and environment—will not.

Thank you for your continued confidence in NorthWestern Energy.

As a shareholder, we encourage you to read this proxy statement, vote on the proposals before you, and attend the virtual annual meeting, which will be held on Thursday, April 30, 2026, at 10:00 a.m., Mountain Daylight Time at www.virtualshareholdermeeting.com/NWE2026.

Proxy Summary

Items of Business

2025 Executive Pay Overview

Alignment of Pay with Shareholder and Customer Interests

Our executive pay program is designed to align the long-term interests of our executives, shareholders, and customers. The program consists of three core components (base salary, annual cash incentive, and long-term equity incentive), which did not change in 2025. Our annual and long-term incentives continue to be performance-based, and our long-term equity incentive awards continue to be split 70/30 between performance share units with a three-year performance period and restricted share units with a three-year restricted period. To align with market, we also provide a more traditional supplemental retirement cash contribution to our executives, which replaces the executive retirement equity awards we discontinued in 2022. The full design of our compensation program and its components are detailed in the Compensation Discussion and Analysis, beginning on page 33.

The performance-based incentive awards and time-based equity award place asignificant percentage of executive compensation at risk— approximately 80 percent of the compensation of our Chief Executive Officer (CEO) and roughly 60 percent of the compensation of our other named executive officers (NEOs). Our Board establishes the metrics and targets for these incentive awards based on advice from the Compensation Committee’s independent compensation consultant, WTW. The 2025 LTIP performance metrics did not change from 2024, although we did update the targets associated with those metrics.

We also require our executives to retain meaningful ownership of our stock (ranging from 2x to 6x their annual base salary). This structure encourages our executives to focus on both short- and long-term performance and rewards our executives, shareholders, and customers when we achieve our financial and operating objectives. We believe our compensation program is fair to all employees, as evidenced by our relatively low CEO to median employee pay ratio for 2025 of 37:1. For 2024, the average CEO to median employee pay ratio for our peers was 41:1, ranging from 15:1 to 81:1.

Performance Against Incentive Targets

We believe 2025 was critical in setting the stage for future growth for our Company. In August, we announced our pending merger of equals (the Merger) with our peer, Black Hills Corporation. The Merger will allow two companies with shared legacies and commitments to customers and communities to operate on a larger scale, capture

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Proxy Summary

efficiencies, and execute on growth opportunities. We also completed our acquisition of the Energy West natural gas distribution assets in Montana, adding additional utility infrastructure to our operations. We also focused on (a) preparing for the January 1, 2026, acquisition of additional ownership interests in the Colstrip Generating Station (with a zero-dollar acquisition price), to improve our generation capacity and (b) capturing future growth through providing service to large-load data center customers.

From a financial perspective, our net income decreased from the prior year, and, for the three-year period ended December 31, 2025, we achieved an ROAE of 7.4 percent, an EPS growth rate of 1.2 percent, and our TSR was 25.0 percent (as calculated for our long-term incentive awards). Operationally, we worked safely and provided highly reliable service to our customers. Additionally, our customer satisfaction performance exceeded target. In total, we achieved below target performance for our 2025 annual incentive awards and above target performance for our long-term incentive awards that vested in 2025 following certain discretionary adjustments approved by our Board. We provide further details regarding these awards and how performance is calculated and adjusted in the Compensation Discussion and Analysis.

Shareholder Feedback on Executive Pay

At our 2025 virtual annual meeting, shareholders approved our 2024 NEO pay by 98.3 percent of the votes cast. In light of this overwhelming approval, we continue to operate within the same general parameters our shareholders previously approved, with the limited exceptions highlighted above and discussed in this proxy statement.

Pay Versus Performance

Based on the information in our Pay Versus Performance disclosure, beginning onpage 61, the compensation actually paid (CAP) to our CEO and other NEOs in 2025 was more than the compensation disclosed in the Summary Compensation Table. CAP appears to correlate with certain measures of corporate performance — CAP appears to increase or decrease with increased or decreased TSR, which is not surprising as a third of our LTIP awards are tied to relative TSR. However, CAP does not appear to correlate with certain other measures of corporate performance — CAP increased and decreased from year to year even though net income consistently increased until this past year, and our supplemental Company selected metric (three-year ROAE) remained relatively flat. This result also is not surprising because these metrics represent a smaller percentage of our incentive compensation.

Corporate Governance Overview

Corporate Governance is a pillar at NorthWestern Energy Group, Inc., and we believe our governance practices are sound, as demonstrated by our ranking from Moody’s Investor Service as the 5th best utility for governance practices. We provide details of our governance practices in the Corporate Governance section of this proxy statement.

We are nominating nine individuals for election as director, all of whom were elected by shareholders at last year’s annual meeting by an average of 99.6 percent of the votes cast. Each of the nominees is independent, with the sole exception of our CEO. We consider our Board to be diverse from several perspectives, as detailed in the Biographies of Our Nominees provided later in this proxy statement.

Our Board is led by an independent chair, and our four Board committees – Audit, Compensation, Governance, and Operations – are chaired by and composed entirely of independent directors.

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Items of Business

Proposal No. 1

Election of Directors

Our Board is nominating nine people for election as directors at the 2026 annual meeting. All nominees currently serve as a director of our Board. Elected directors will serve for one year, until the next annual meeting of shareholders (or until a successor is able to serve) or, if earlier, the consummation of the Merger. Our diverse slate of nominees is listed below, and we provide additional background information and individual qualifications for each nominee in the Corporate Governance—Individual Directors section of this proxy statement, beginning onpage 20.

The Board of Directors recommends you vote “FOR” each of the nine director nominees.

Unless you specifically withhold your authority to vote for the election of directors, the persons named in the accompanying proxy intend to vote “FOR” the election of each of the following director nominees:

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Items of Business

All nominees have advised the Board that they are able and willing to serve as a director. Although not anticipated, if any nominee becomes unavailable for any reason, the shares represented by the proxies may be voted for such other person or persons as may be determined by the holders of the proxies (unless a proxy contains instructions to the contrary). In no event will the proxy be voted for more than nine nominees.

Board Nomination Process

Our Governance Committee leads the Board in a director succession planning process to allow for a smooth and gradual transition from our longer tenured directors, while preserving the culture of the Board. This process includes a review of individual skill sets and tenures of current members and considers additional attributes that could be beneficial for the Board in the future, with a particular focus on Company strategy, emerging risks, and a diversity of perspectives.

When selecting the current slate of nominees, the Board concluded the nominees bring a diverse and extensive professional experience providing a broad collective skill set that is advantageous to the oversight of the Company. While the industry-specific expertise possessed by certain of the nominees is essential, we also will benefit from the viewpoints of directors with expertise outside our industry which expand the Board’s ability to provide relevant guidance to our business.

Our Board recommends a vote “FOR” election of each of the nominees.

Directors will be elected by a favorable vote of a plurality of the shares present online at the virtual annual meeting or represented by proxy and entitled to vote at the virtual annual meeting. You may vote “FOR” all of the nominees, or you may “WITHHOLD AUTHORITY” for one or more of the nominees. Withheld votes will not count as votes cast for the nominee but will count for purposes of determining whether a quorum is present. Shareholders do not have the right to cumulate their vote for directors. If your shares are held through a broker, bank, or other nominee and you do not vote your shares, your bank, broker, or other nominee may not vote your shares in this proposal, as it is considered a “non-routine” matter. Abstentions or broker non-votes as to the election of directors will not affect the election of the candidates receiving a plurality of votes; however, under our Majority Plus Resignation Vote Policy described onpage 25 of this proxy statement, if a nominee for director receives more “WITHHOLD AUTHORITY” votes than “FOR” votes, such nominee shall immediately tender his or her resignation under the procedures in the policy.

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Items of Business

Proposal No. 2

Ratification of Deloitte & Touche LLP as the Independent Registered Public Accounting

Firm for 2026

Our Audit Committee oversees the integrity of our accounting, financial reporting, and auditing processes. To assist with these responsibilities, the Audit Committee has appointed Deloitte as our independent registered public accounting firm to audit our financial statements for 2026. The Board is asking you to ratify the committee’s decision at the annual meeting. The Board values your input on the committee’s appointment of Deloitte, but approval by shareholders is not required by law. If shareholders do not ratify the appointment of Deloitte, the committee will reconsider its selection. Regardless of the voting result, the committee may appoint a new firm at any time if it believes a change would be in the best interests of the Company and its shareholders.

The Board of Directors recommends you vote “FOR” the ratification of Deloitte & Touche LLP as the independent registered public accounting firm for 2026.

Deloitte representatives will be present at the annual meeting. They will have the opportunity to make a statement if they desire to do so and are expected to be available to respond to appropriate questions.

Description of Audit Fees

The table below presents a summary of the fees paid to Deloitte for professional services for the fiscal years ended December 31, 2024, and 2025.

Audit-related feesare fees billed for assurance and related services that are reasonably related to the performance of the audit of our financial statements and are not reported under “Audit Fees.”

Tax feesare fees billed for tax compliance, tax advice, and tax planning.

All other fees are fees for products and services other than the services reported above.

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Items of Business

Pre-approval Policies and Procedures

SEC rules require public company audit committees to pre-approve audit and non-audit services. Our Audit Committee follows procedures pursuant to which audit, audit-related, tax, and all permissible non-audit services are pre-approved by category of service. The fees are budgeted, and actual fees versus the budget are monitored throughout the year. Circumstances may arise when it becomes necessary to engage the independent public accountants for additional services not contemplated in the pre-approved budget. In those instances, we obtain pre-approval of the Audit Committee before engaging independent public accountants. The procedures require the Audit Committee to be informed of each service, and the procedures do not include any delegation of the Audit Committee’s responsibilities to management. The Audit Committee may delegate pre-approval authority to one or more of its members; the member to whom such authority is delegated will report any pre-approval decisions to the Audit Committee at its next scheduled meeting.

Pursuant to the provisions of the Company’s Audit Committee Charter, before Deloitte is engaged to render audit or non-audit services, the Audit Committee must pre-approve such engagement. For 2025, the Audit Committee (or the Chair of the Audit Committee pursuant to delegated authority) pre-approved 100 percent of the audit, audit-related, tax, and other fees.

Leased Employees

In connection with their audit of our 2025 annual financial statements, more than 50 percent of Deloitte’s work was performed by full-time, permanent employees of Deloitte.

The affirmative vote of the holders of a majority of the shares present online at the virtual annual meeting or represented by proxy and entitled to vote at the virtual annual meeting is required to ratify the appointment of Deloitte as our independent registered public accounting firm for 2026. If voting instructions are not provided, brokers may vote a client’s proxy in their own discretion on this proposal, as it is considered a “routine” matter. Abstentions will have the same effect as a vote against the proposal. Unless instructed to the contrary in the proxy, the shares represented by the proxies will be voted “FOR” the proposal to ratify the selection of Deloitte to serve as the independent registered public accounting firm for NorthWestern Energy for the fiscal year ending December 31, 2026.

Audit Committee Report

In the performance of the Audit Committee’s oversight function, and in connection with the December 31, 2025, financial statements, the Audit Committee reviewed and discussed the audited financial statements with management and Deloitte. It discussed the matters required by the applicable requirements of the PCAOB and the SEC. The Audit Committee received the written disclosures and the letter from Deloitte, our independent registered public accounting firm, required by applicable requirements of the PCAOB regarding the independent accountant’s communications with the Audit Committee concerning independence; and it has discussed with Deloitte the firm’s independence. The Audit Committee considered the compatibility of non-audit services in connection with the auditor’s independence.

Based on the Audit Committee’s review of the consolidated financial statements and discussions with and representations from management and Deloitte referred to above, it recommended to the Board that the audited financial statements be included in our Annual Report on Form 10-K for the year ended December 31, 2025, filed with the SEC.

Audit Committee

Jeffrey Yingling, Chair Dave Goodin

Jan Horsfall Kent Larson

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