The lieutenant governor of Michigan, Garlin Gilchrist II, announced on Tuesday that he is running for governor, joining a competitive Democratic primary field at a time of uncertainty for the party in that swing state and beyond.

Mr. Gilchrist, a software engineer from Detroit, has been a visible second-in-command to Gov. Gretchen Whitmer over the last six years, presiding over the State Senate, leading a panel that studied racial disparities during the Covid-19 pandemic and signing some bills into law.

Still, Mr. Gilchrist is not exactly a household name, and with more than a year before the 2026 primaries, he must introduce himself to more voters and compete with other prominent Democrats for endorsements and donors. Secretary of State Jocelyn Benson, who has emphasized voting rights and democracy, and Sheriff Christopher R. Swanson of Genesee County, who spoke at last year’s Democratic National Convention, have already entered the race, and others could follow. Ms. Whitmer is barred by term limits from seeking re-election.

Michigan’s eventual Democratic nominee could face a difficult three-way race in the general election. Mayor Mike Duggan of Detroit, a longtime Democrat, is running for governor as an independent, a move that some Democrats worry could give the Republican candidate an advantage. Aric Nesbitt, the Republican leader in the Michigan Senate, is seeking his party’s nomination, and other candidates could still enter that race.

In an interview, Mr. Gilchrist, 42, said he planned to focus on housing and health care issues on the campaign trail, though he declined to outline specific policy proposals. He also criticized President Trump’s tariffs, which he said had the potential to “be catastrophic for industries across Michigan,” and described how he would approach governing with Mr. Trump in office.

“You’ve got to play defense to stop the other team from scoring and hurting people, but you also recognize that sometimes the best defense is a good offense,” Mr. Gilchrist said. “And you’ve got to understand when we can go on the attack and really call out, push back on things in the administration.”

Ms. Whitmer, who built a national profile after winning a competitive Democratic nominating contest in 2018, has indicated to local reporters that she does not plan to endorse a candidate in next year’s primary. After engaging in repeated disputes with Mr. Trump during his first term, during which she tied his rhetoric to a plot to kidnap her, Ms. Whitmer has taken a more conciliatory approach this time, signaling a willingness to work with the president on areas of agreement.

Michigan is a closely divided state whose voters have supported both Democrats and Republicans in recent years. Last year, Mr. Trump carried the state and Republicans flipped control of the Michigan House of Representatives even as voters elected Elissa Slotkin, a Democrat, to the U.S. Senate.

In addition to selecting a governor, Michigan voters will choose a new senator next year. The Democratic incumbent, Gary Peters, is not running for another term.

Mr. Gilchrist, who is married with three children and who would be Michigan’s first Black governor, tied his party’s losses in 2024 to voters who were “mad about the status quo and didn’t feel like Democrats were necessarily, across the board, matching their energy and matching that anger.” He said his candidacy would respond to that frustration.

“I am a person who is ready to get in there and do something and deliver results and solve problems,” he said.