NISOURCE INC.

This summary highlights information that may be expanded upon elsewhere in this proxy statement (“Proxy Statement”). This summary does not contain all of the information that you should consider, and you should read the entire Proxy Statement before voting. The accompanying proxy is solicited on behalf of the Board of Directors of NiSource Inc. (the “Board”) for the 2026 annual meeting of stockholders (the “Annual Meeting”).

2026 Annual Meeting of Stockholders

VOTING

Each share is entitled to one vote for each director to be elected and on each matter to be voted upon at the Annual Meeting.

This Proxy Statement and the accompanying proxy card are first being sent to stockholders on March 30, 2026.

WHO WE ARE

NiSource is one of the largest fully regulated utility companies in the United States, serving approximately 3.8 million natural gas and electric customers across six states, Indiana, Ohio, Pennsylvania, Maryland, Virginia and Kentucky, through our local Columbia Gas and NIPSCO brands. We are based in Merrillville, Indiana, and have approximately 7,700 employees focused on safely delivering reliable and affordable energy to our customers and the communities we serve. We have a vision to be a premier, innovative and trusted energy partner and we exist to deliver safe, reliable energy that drives value to our customers.

We use the terms “NiSource,” the “Company,” “we,” “our” and “us” in this Proxy Statement to refer to NiSource Inc.

VOTING MATTERS AND BOARD RECOMMENDATIONS

NISOURCE INC. 2026 PROXY STATEMENT

PROXY STATEMENT SUMMARY

BOARD OF DIRECTORS NOMINEES

Director Nominees (12)

See “Proposal 1 – Election of Directors” for more information on our director nominees.

NISOURCE INC. 2026 PROXY STATEMENT

PROXY STATEMENT SUMMARY

GOVERNANCE HIGHLIGHTS

Annual election of directors

Majority voting for all directors with resignation policy

No supermajority voting provisions

No stockholder rights plan (“poison pill”)

Proxy access by-law (3% ownership / 3 years duration / up to 20 stockholders / 20% of board)

Stockholder right to call special meetings

Separate chair and CEO

All directors independent, except CEO

Board committees comprised of all independent directors

Regular executive sessions of independent directors

Annual Board and committee evaluation process and ongoing evaluations of individual directors

Strategic and risk oversight by Board and committees

Annual “Say-on-Pay” advisory votes

Strong alignment between pay and performance in incentive plans

Commitment to safety and customer experience

Political contributions disclosure

Enhanced independent registered public accounting firm disclosure

Publication of annual sustainability report

See “Corporate Governance” for more information on our corporate governance practices.

EXECUTIVE COMPENSATION HIGHLIGHTS

We have designed our executive compensation program to meet our business objectives, including attracting and retaining top-level executive talent, using various compensation elements and to align executive pay with the long-term and short-term interests of our stockholders. We received approximately 97% stockholder support for our Say-on-Pay vote in 2025. We recognize and reward our executive officers through compensation arrangements that link their pay to the Company’s performance, and we seek to ensure an alignment of interests with our stockholders, by including a significant portion of total compensation consisting of at-risk performance-based compensation.

See “Compensation Discussion and Analysis (CD&A)” and “Components of 2025 Executive Compensation” for more information on our executive compensation program.

NISOURCE INC. 2026 PROXY STATEMENT

PROXY STATEMENT SUMMARY

ECONOMIC, ENVIRONMENTAL AND SOCIAL HIGHLIGHTS

We are focused on helping ensure the work we do satisfies long-term energy needs in a way that balances the interests of our stakeholders. Guiding principles that shape and inform how we make many of our decisions include, but are not limited to:

We announced a goal of net zero GHG emissions by 2040 covering both Scope 1 and Scope 2 GHG emissions (“Net Zero Goal”). Our Net Zero Goal builds on GHG emission reductions achieved to-date. We plan to achieve our Net Zero Goal primarily through the continuation and enhancement of existing programs, such as retiring and replacing coal-fired electric generation with low- or zero-emission electric generation, ongoing pipe replacement and modernization programs, and deployment of advanced leak-detection technologies. In addition, we plan to advance other low or zero-emission energy resources and technologies, which may include hydrogen, renewable natural gas, long-duration storage, and/or deployment of carbon capture and utilization technologies, if and when these become technologically and economically feasible. Carbon offsets and renewable energy credits may also be used to support achievement of our Net Zero Goal. Our GHG emissions projections, including achieving a Net Zero Goal, are subject to various assumptions that involve risks and uncertainties, and did not include any assumptions related to data center development and associated load growth. We remain committed to our Net Zero Goal; however, certain of our interim goals may evolve as we assess and respond to business opportunities such as data centers. Achievement of our Net Zero Goal by 2040 will require supportive regulatory and legislative policies, favorable stakeholder environments and advancement of technologies that are not currently economically or technologically feasible to deploy at scale, as well as execution of our business plan.

We are keenly aware that in addition to being a business entity, we are also a social and community enterprise that includes our employees, partners, customers and the communities we serve. For more information about our business and strategy and about our corporate responsibility and sustainability efforts, see our 2025 Annual Report on Form 10-K and our website atwww.nisource.com.

GENERAL INFORMATION

Stock Symbol: NI

Stock Exchange: New York Stock Exchange (“NYSE”)

Registrar and Transfer Agent: Computershare Investor Services

State of Incorporation: Delaware

Corporate Headquarters: 801 E. 86 th Avenue, Merrillville, Indiana 46410

Corporate Website: www.nisource.com

NISOURCE INC. 2026 PROXY STATEMENT