Sen. Hart at McKeon Post meeting on UMass plans to build dorms, March 2003: His opposition to building student housing at UMass Boston was pivotal. Photo by Bill Forry

State Sen. Jack Hart’s plan to decamp for a law firm this week rocked the Boston political scene when the news broke Monday night. The 51-year-old South Boston Democrat will leave a void within the Boston delegation on Beacon Hill after spending 16 years under the golden dome, five of them as a state representative.

As Hart prepares to leave the Senate tomorrow and begin work at Nelson Mullins’ Boston office on Monday, he is hearing warm words come his way from City Hall and the State House.

At Faneuil Hall on Tuesday night, he received a shout-out from Mayor Thomas Menino in his State of the City address. “I’m going to miss you, Jackie,” Menino said, with Hart sitting nearby, behind Gov. Deval Patrick.

Congressman Stephen Lynch, who lives on G St., across the street from Hart, said he was “melancholy” about Hart leaving. “I’ve watched his kids grow,” Lynch said after Menino’s speech. “We came into politics together, only separated by a few months, he and I. And I’ll miss him, you know. I don’t know if I’m sad or I’m jealous. I wish him and his family the best.”

Senate President Therese Murray, a Plymouth Democrat who is a Dorchester native, told the State House News Service that the decision for Hart was “agonizing” because he liked working in the Senate. “He was born in Southie. You’re born in Southie, politics is part of your life. He didn’t want to disappoint anyone but he has to look out for his family. He has four daughters and you know schooling costs, even though he is working two jobs and his wife works.”

In a release announcing Hart’s hiring, the law firm noted that he helped with the master planning for the South Boston waterfront and “championed” the Boston Convention and Exhibition Center.

Hart has had a complicated relationship with UMass Boston, helping the Columbia Point commuter campus secure capital funding while questioning its desire to build dormitories for students.

“They need to come out to the neighborhood and convince them it’s a good thing,” Hart said in 2011. “Until they do that, it is not a done deal.”

He has also organized annual clean-ups of Dorchester and South Boston beaches and helped grab funds for improvements to the stretch of the Red Line running through the neighborhood, and the Fairmount Line, which is adding stations in Dorchester and Mattapan.

“Sen. Hart has done a great job,” said state Rep. Linda Dorcena Forry of Dorchester. “It will be a great loss.” State Rep. Russell Holmes of Mattapan added, “It’s often people say, ‘Let’s call Jack,’ around an issue. I respect that Jack had to make a tough decision.”

Fellow South Bostonians were as effusive in their praise of Hart as their Dorchester counterparts. All could be candidates to succeed him in the state Senate. State Rep. Nick Collins, who once worked for Hart, said he considered the outgoing senator a mentor. “He’s going to leave a great legacy of public service,” Collins said. “I think most of all, Jack will be leaving a legacy of a gentleman who never forgot where we came from.”

In a statement, former Mayor Ray Flynn said Hart’s “effective leadership” will be “deeply missed” as South Boston goes through a period of rapid change, an allusion to the steady gentrification of the neighborhood and a burgeoning Seaport District. “We wish him success and happiness,” Flynn said.