Mayor Thomas M. Menino will announce at a Faneuil Hall event Thursday afternoon that he will not seek a sixth term in office, according to officials familiar with his decision.
Menino arrived at his decision late last week and reconsidered it for the last several days to be sure he felt comfortable following through, the officials said.
He plans to tell most of his aides and advisers Thursday morning.
A grim mood rippled through City Hall on Wednesday afternoon as municipal workers speculated about what could be coming. Menino has never used Faneuil Hall as a venue to launch a reelection bid. His political organization has not pushed to get people to the event the way it does for a campaign rally, several people in City Hall said. There has been no mobilization of city employees asked to take vacation time, a normal precursor to major political appearances.
Rumors ran rampant in political circles. Phone calls and text messages flooded elected officials who have been mentioned as potential mayoral candidates. Several people with deep roots in Boston politics said they have spoken to Menino confidantes and were told the mayor had decided not to run.
The 70-year-old mayor, who has been in office for nearly two decades, stayed largely out of sight Wednesday and did not schedule any public events. In recent months, Menino has endured a string of illnesses that left him hospitalized for eight weeks at the end of last year. He was initially diagnosed with blood clots and a severe respiratory infection, and doctors later determined he fractured a vertebra and had type 2 diabetes.
Earlier this week, Menino delivered a robust speech that sounded almost like a pitch for reelection. But as the room emptied, Menino told lingering reporters he felt “at peace about where the city is going.”
While Menino weighed whether to run again, potential mayoral candidates have remained on the sidelines, loath to challenge the five-term incumbent. Those who have said they might run for an open seat include state Representative Martin J. Walsh of Dorchester and city councilors Rob Consalvo and Tito Jackson.
Only one major candidate -- City Councilor John R. Connolly -- has launched a campaign and vowed to run, regardless of Menino’s decision. Two other candidates have said they are running for mayor, but they have raised almost no money for a campaign. One is Will Dorcena, who won less than 5 percent of the vote when he ran in 2011 for an at at-large seat on the City Council. The other is Charles Clemons, co-founder of TOUCH 106.1 FM.
On April 17, candidates can begin applying for nomination papers, the first step in getting their name on the ballot for the preliminary election, scheduled for Sept. 24. The top two vote-getters will compete Nov. 5.
Menino’s departure will do much more than trigger the first open mayor’s race since 1983. It will mark the end of an era, a watershed moment in Boston akin to Ted Williams’ retirement after his two-decade run at Fenway Park.
Starting as acting mayor on July 12, 1993, Menino took office as a relatively unknown 50-year-old city councilor from Hyde Park. Candidates vying for the mayor’s post dismissed Menino as a caretaker keeping the seat warm until the November election.
Menino proved them wrong, maximizing the power of the office to run as an incumbent and win a resounding victory. He will now leave City Hall early next year, at age 71, the only mayor a generation of Bostonians have ever known, the man who guided the city into the new millennium and set its course for decades to come.
Rivals often underestimated Menino because of his clumsy speech and everyman appearance, but he proved to be the shrewdest politician of his generation. Menino ruled with iron determination, but could be famously thin skinned.
Menino commanded a get-out-the-vote machine that has made his endorsement the most coveted in Massachusetts, attracting aspiring governors, senators, and other candidates eager for his help.
Unlike many other longtime big city mayors, Menino’s administration remained largely untainted by scandal.
Menino may be best known as the “Urban Mechanic,” who made a career of the politics of filling potholes, fixing broken street lights, and racing tirelessly from ribbon cutting to ribbon cutting.
His focus on minutiae more suited to a district city councilor was sometimes disparaged by critics who said he lacked a sweeping vision for the city.
“What is a vision?” Menino asked the Boston Globe Magazine in a 1994 profile. “Sometimes we get caught up in the grandiose. My vision is jobs, a better school system, community policing, health care. When I leave this job, I want the city to be in better shape than when I took it over.”
Two decades later, Menino’s vision has reshaped the city in ways large and small, from an edict against flat roofs on Back Bay skyscrapers to the look of doorways in Dorchester. He will leave office in the midst of an extraordinary building boom, with a new neighborhood exploding in the Seaport, renewed vibrancy in the Fenway, and the construction of a municipal building designed to anchor the transformation of Dudley Square.
Menino has championed more resources for the homeless, pushed nationally to curb gun violence, and became an early -- and staunch -- defender of gay marriage. Before he was mayor, he advocated for distribution of condoms and care for people with AIDS at a time when the disease was still seen as a scourge.
“If I weren’t a councilor, I would be a social worker,” Menino told the Globe in 1993. “All I’m really interested in is doing things that help people. I really care about the lives of people in the city.”
Jim O’Sullivan of the Globe staff contributed to this report. Andrew Ryan can be reached at email@example.com Follow him on Twitter @globeandrewryan.