Exhibit 23

CONSENT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

We consent to the incorporation by reference in Registration Statement No. 333-234422 on Form S-3, Registration Statement Nos. 333-107743, 333-166888, 333-204168, and 333-233382 on Form S-8, and Registration Statement Nos. 333-228790 and 333-228791 on Form S-4of our reports dated February 27, 2020, relating to the financial statements of NiSource Inc. and subsidiaries (the “Company”) and the effectiveness of the Company’s internal control over financial reporting appearing in this Annual Report on Form 10-K for the year ended December 31, 2019.

/s/ DELOITTE & TOUCHE LLP

Columbus, Ohio

February 27, 2020