In his first formal endorsement since leaving City Hall and the Biden administration, Marty Walsh is backing John FitzGerald in the race to replace Frank Baker, who isn't running for reelection after spending more than a decade as District 3’s councillor.

FitzGerald, 41, is a son of the late Mission Hill state Rep. Kevin Fitzgerald, who served with Walsh in the state Legislature and died of cancer in 2007. When Walsh was first elected as a Dorchester state representative in 1997, he and Rep. Fitzgerald shared an office. “Kevin was a mentor to me,” Walsh told the Reporter on Sunday.

“I watched John FitzGerald grow up,” said Walsh, who served as President Biden’s labor chief before leaving earlier this year to take a job as head of the NHL players union. “He’d be a great city councillor for Dorchester. His family’s very much into public service.”

FitzGerald, who is one of seven candidates vying for Baker's seat, held various roles in Walsh’s mayoral administration and the Boston Planning and Development Agency (BPDA). He served as a city liaison when Boston unsuccessfully sought the 2024 Summer Olympics, and he was involved in the planning effort known as Image Boston 2030. He currently works as the BPDA’s deputy director of real estate operations.

In a statement, FitzGerald called Walsh the “definition of a public servant.” “I had the privilege of working for him at Boston City Hall, where I saw up close his commitment to helping every resident and his determination to make our city the best it can be,” he added. “He has been and continues to be a true example for me, and I could not be more honored by his support.”

FitzGerald, who capitalizes the G in his surname in a nod to his paternal grandfather, moved to Adams Village a decade ago. He and his wife Meghan, a Quincy Public Schools teacher, have three children.

The list of candidates running to replace Baker also includes Meetinghouse Hill activist Jennifer Johnson; former government aide and schoolteacher Barry Lawton of Uphams Corner/Savin Hill; Savin Hill labor lawyer Matt Patton; Fields Corner teacher and pastor Joel Richards; former education nonprofit leader Ann M. Walsh of Lower Mills; and housing activist Rosalind Wornum of Ashmont. (Marty Walsh is unrelated to candidate Walsh, who lives just a few doors down from the former mayor.)

District 3 is anchored in Dorchester, with the boundaries beginning at the Neponset River and running all the way to the South End’s Herald Street.

“When people endorse candidates, sometimes it’s by name only. I’m going to be helping John as much as I can,” said Walsh, who also was a top labor leader before he won the 2013 mayoral election. “I don’t like to endorse in name only. I get a little more engaged.”

Walsh already has a FitzGerald campaign sign on his front lawn, placed there just before the July 4th holiday. He plans to go door-knocking with FitzGerald and to donate to the campaign’s coffers.

FitzGerald led the field in fundraising for June, pulling in $54,000. He had nearly $59,000 in cash on hand at the end of the month, according to publicly available campaign finance records. Donors included former House Speaker Tom Finneran; Lorrie Higgins, Walsh’s longtime partner, former Lt. Gov. Thomas O’Neill, former state Rep. Jeff Sanchez, and former Councillor Michael Ross. Ross and Sanchez recently co-hosted a FitzGerald fundraiser at the offices of the Prince Lobel law firm.

Ann Walsh raised just over $22,000, and has $19,440 in cash on hand, while Patton raised $7,719, and has $25,221. Richards raised $6,134 and has $33,034 on hand; Lawton raised $4,418 and has $3,230; and Johnson raised $1,113 and has $14,053. Wornum has not filed any fundraising reports.

The preliminary, which will narrow the field to two candidates, is scheduled for Sept. 12.

On Sunday, Walsh hinted at other endorsements to come later this election season. He stayed away from public endorsements during the 2021 mayoral race, citing the federal Hatch Act, which prohibits certain government officials from supporting candidates.

During his time in City Hall, Walsh stepped into multiple campaigns at the local, state and federal level, with limited success. In one election cycle, he backed incumbent Congressman Michael Capuano, who was toppled by Ayanna Pressley, and supported then-state Rep. Dan Cullinane of Dorchester, who beat back a challenger.

As a state lawmaker, Walsh backed Baker’s bid for City Council in 2011. The open race — the result of Maureen Feeney deciding not to seek reelection — became a war of proxy between Walsh, who has known Baker since childhood, and Mayor Thomas Menino, who backed Cedar Grove civic activist John O’Toole.

As for this year’s District 3, “I think it’s going to be a good old-fashioned Dorchester race,” Walsh predicted. “District 3 generally has good races; people knock doors and go out and do their thing. That’s going to be John Fitzgerald’s campaign.”