Maya Rockeymoore Cummings, a policy consultant and chair of the Maryland Democratic Party, will run for the congressional seat vacated by her husband, Representative Elijah E. Cummings, who died last month. “I am, of course, devastated at the loss of my spouse, but his spirit is with me,” she told The Baltimore Sun on Monday. “I’m going to run this race and I’m going to run it hard, as if he’s still right here by my side.”

Mr. Cummings, who died in October at age 68, had represented Baltimore’s Seventh Congressional District for 13 terms beginning in 1996, and rose to become among the House’s most powerful Democrats. Mr. Cummings was a leading Democrat in the impeachment investigation of President Trump, and his funeral was attended by thousands of mourners, many who praised him as a champion of civil rights and working people.

Ms. Rockeymoore Cummings, 48, who founded the consulting firm Global Policy Solutions, said she would resign as chair of the state party, a role she held for a year.

She ran for governor of Maryland in 2017 but dropped out in January 2018, citing Mr. Cummings’s failing health. Ms. Rockeymoore Cummings holds a doctorate in political science from Purdue University, and was a legislative aide on Capitol Hill, at the National Urban League and for the Congressional Black Caucus Foundation.

Mr. Cummings told her six months ago that he wanted her to take over his seat, she said on MSNBC’s “The Rachel Maddow Show” on Monday. Ms. Rockeymoore Cummings said she had “fought right alongside Elijah for the last 12 years.”

“I believe very strongly that I have the background, and the focus, and the commitment, and the ability to take the reins and to make a good run for this seat,” she said.

A special election is planned for April 28, 2020, with primaries on Feb. 4. Several Democrats have already announced plans to run for the seat.

Ms. Rockeymoore Cummings told The Sun that she planned to have a preventive double mastectomy on Friday, taking her off the campaign trail for as much as four weeks.