Thomas N. O’Brien, a developer and former chief planner for the city of Boston under the late Mayor Tom Menino, will not run for Mayor of Boston, according to a statement released by a spokesman today.

“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 through a statement sent to reporters this afternoon. “Instead, I will continue my work with The HYM Investment Group and my engagement in Boston’s charitable and civic life."

He added: “My commitment to Boston remains unwavering. 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’s candidacy may have significantly changed the dynamics in a mayoral race that is still taking shape with incumbent Mayor Michelle Wu expected to formally launch her own re-election bid in the coming days.

Josh Kraft, a longtime non-profit executive and scion of the Kraft sports empire family, launched his own campaign for the seat in January. Domingos DaRosa, who has run unsuccessfully for city council on three occasions in recent election cycles, also formed a committee to seek the mayoral job.

A South Shore native who lives in the city with his wife Patricia and five children, O’Brien, 61, is currently the managing partner of HYM Investment Group, a development firm that has built-out some of the city’s most high-profile buildings in recent years, including the Warriors Ice Arena and adjacent buildings in Allston’s Boston Landing and the Parcel 3 building in Roxbury. His company is currently leading the redevelopment of Suffolk Downs, the 161-acre former horse racing site in East Boston, which could yield 10,000 new units of housing if built as planned.

Prior to entering private real estate, O’Brien served as the director of the Boston Redevelopment Authority from 1993 to 1999. The authority is now known as the Boston Planning Agency. His biography on the HYM website says O’Brien has been a strong advocate for immigrant rights and is a board member of several organizations, including the Pine Street Inn, the Rose Kennedy Greenway Conservancy, and the Anti-Defamation League of New England. A member of the Massachusetts Bar Association, O’Brien is a graduate of Brown University and Suffolk Law.

Mayoral hopefuls must gather 3,000 signatures from registered Boston voters to make the ballot. Nomination papers will not be available from the city’s Election Department until April 16 with a May 20 deadline to turn them in for certification.

The preliminary municipal election is set for Tuesday, Sept. 9. The top two finishers in that election would compete in the final election on Tuesday, Nov. 4.

The only public polling published — conducted by Emerson College Polling Center in late February—showed Mayor Wu with a strong early lead over Kraft, 43-29 with about 24 percent undecided. The polling took place before Wu made a nationally-publicized appearance before a Congressional committee that grilled her and other big city mayors on immigration policies and enforcement.

In a statement released by the his campaign after O'Brien's statement, Josh Kraft said, “I understand that running for office is a deeply personal decision. I have great respect for Tom and his commitment to many community organizations.”