DEVELOPER TOM O’BRIEN has opted against a run for mayor of Boston, leaving the field to Mayor Michelle Wu and other challengers hoping to topple the first-term incumbent. 

His abrupt reversal comes after his entry into the race was all but assured last week, as both Politico Massachusetts and The Boston Globe reported that he planned to launch his campaign in the coming days. O’Brien had been making phone calls to set up a mayoral campaign while on a pre-planned family trip to Ireland. 

O’Brien’s friends and acquaintances said he has long wanted to run for mayor of Boston. O’Brien served under the late Mayor Thomas Menino at the Boston Redevelopment Authority, and for the last 16 years, he has worked at HYM Investment Group, where he is the CEO and a founding partner. 

The company has been involved in real estate projects across the city, including redeveloping the Suffolk Downs horse racetrack on the East Boston-Revere border and One Congress, a new office building by City Hall that has as its main tenant State Street, the financial services company. 

“After many conversations with people I know, trust and admire, I’ve decided not to pursue a political candidacy at this time,” O’Brien said in a statement Monday. “Instead, I will continue my work with The HYM Investment Group and my engagement in Boston’s charitable and civic life.” 

“I’ll keep working to make our city a more affordable, inclusive and vibrant place to live, work and thrive — and I look forward to partnering with Mayor Wu, her administration and others to help achieve that vision,” O’Brien added. 

O’Brien did not mention who will get his vote later this year. His exit leaves Wu and Josh Kraft, the philanthropist son of New England Patriots owner Robert Kraft, as the two main contenders for the job. Kraft has criticized Wu over bike lanes, while Wu has hit Kraft for launching a mayoral campaign after living in the city for little more than a year, having moved into Boston’s North End from Newton. 

Kraft launched his campaign in February and has raised $570,000. 

In his own statement, Kraft acknowledged O’Brien’s exit and said he has “great respect” for O’Brien and “his commitment to many community organizations.” 

Domingos DaRosa, a Hyde Park community activist, has also set up a mayoral campaign. North End restaurateur Jorge Mendoza Iturralde and perennial political candidate Althea Garrison have expressed interest in a run for mayor. 

Wu plans to formally kick off her reelection campaign on April 5 at the Cyclorama in Boston’s South End. 

Inside a small Colombian restaurant in East Boston, hours before O’Brien changed his mind about running, Wu rolled out endorsements from local elected officials, including state Sen. Lydia Edwards, state Rep. Adrian Madaro, and City Councilor Gabriela Coletta Zapata. O’Brien was reportedly planning to kick off his campaign in the neighborhood. 

Asked whether she planned the event to counteract O’Brien’s expected entry, Wu said her campaign has held several similar endorsement events and “sometimes timing works out.” 

“We’ll see what happens,” she said of O’Brien. “Elections are really important. It’s a time for everyone to come together and talk about the needs in our community, and present the vision that they have, and engage with residents about what we need to see in the future. I don’t think Boston wants a developer as our mayor.” 

Four hours later, O’Brien was out.