NISOURCE INC.

The accompanying proxy is solicited on behalf of the Board for the Annual Meeting to be held on Monday, May 11, 2026 at 10:30 a.m. Central Time, in a virtual format only via live audio webcast at www.virtualshareholdermeeting.com/NI2026. The common stock, $.01 par value per share, of the Company represented by the accompanying proxy will be voted as directed. If you return a signed proxy card without indicating how you want to vote your shares, the shares represented by the accompanying proxy will be voted as recommended by the Board:

This Proxy Statement and the accompanying proxy card are first being sent to stockholders on March 30, 2026. We will bear the expense of this solicitation, which may be supplemented by telephone, facsimile, email and personal solicitation by our officers, employees and agents. To aid in the solicitation of proxies, we have retained D.F. King for a fee of $12,500, plus reimbursement of expenses. We may incur additional fees if we request additional services. We will also request brokerage houses and other nominees and fiduciaries to forward proxy materials, at our expense, to the beneficial owners of stock held as of the close of business on March 16, 2026, the record date for voting.