Stanley C. Rosenberg, who overcame a traumatic youth to become one of the state’s most powerful legislators and used his position to help protect gay marriage, legalize casino gambling, and enact sweeping change to criminal justice laws, announced Thursday that he is resigning in the wake of a damning ethics report about his conduct and judgment.
The Senate accepted the former Senate president’s resignation and endorsed the findings of an investigation that found Rosenberg abrogated his leadership responsibilities by giving his accused serial predator husband, Bryon Hefner, essentially unfettered access to the Senate.
In a statement Thursday, Rosenberg said the investigation “found no conduct by me that violated Senate rules or state ethics law, no evidence that Bryon influenced my actions as Senate president, and no knowledge on my part of any alleged sexual advances, assaults, or attempts by Bryon to influence other senators or staff.”
But the Amherst Democrat, who has served as a legislator for 31 years and whose resignation will take effect Friday at 5 p.m., also expressed grief about the situation.
“I deeply regret the difficulties that this situation has created for the members, the staff, and the institution of the Senate,” Rosenberg said.
The Senate Committee on Ethics investigation was prompted by a Globe story in November. That article reported allegations from four men who said Hefner had sexually assaulted and harassed them and bragged he could influence Senate business.
Senator Michael J. Rodrigues, the committee’s chairman, credited Globe columnist Yvonne Abraham for revealing the alleged wrongdoing. “As painful as this episode is,” he said, “perhaps it was a small step taken in restoring people’s faith in government, and underscoring the importance of a free, open, and accurate media in our society.”
Rosenberg’s announcement followed intense pressure from Governor Charlie Baker, Attorney General Maura T. Healey, and several of his Democratic Senate colleagues who called for him to resign.
“I think it was appropriate for him to step down,” Baker said Thursday. “And I was glad he did.”
According to two people close to Rosenberg, he made the decision to resign in part because he felt his colleagues would move to expel him if he tried to remain. Senators had conveyed to Rosenberg that some staff members said they did not feel safe around him because of his handling of Hefner’s alleged acts of sexual assault.
On Thursday evening, the full Senate adopted a resolution endorsing the findings of the investigation into Rosenberg’s conduct, apologizing to victims and others affected, and pledging “to fortify the Senate’s systems for preventing and intervening in harassment in all its forms.”
While investigators from an outside law firm hired by the Senate found Rosenberg did not break any formal chamber rules, they presented a voluminous case that Rosenberg knew or should have known that Hefner racially and sexually harassed Senate employees — and that Rosenberg failed to address the issue adequately.
They also revealed new allegations of sexual assault against Hefner, who pleaded not guilty last month to multiple criminal charges of sexually assaulting three men and distributing nude photos of a fourth. (Hefner’s lawyer did not respond to an e-mail seeking comment about the report Wednesday.)
Using information gleaned from hundreds of thousands of Senate e-mails and 19,000 text messages, the attorneys determined Rosenberg gave Hefner full access to his official e-mail and did not do enough to prevent Hefner from meddling in Senate business — despite Rosenberg knowing his partner could be “disruptive, volatile, and abusive.”
Rosenberg, who served as Senate president from January 2015 through December 2017, also broke a promise made to his Senate colleagues before he became president that he would separate his personal and professional lives with a firewall, the report put together by Hogan Lovells US LLP found.
His departure marks an astonishing fall from grace for the 68-year-old, who just five months ago was one of the state’s highest-ranking lawmakers and, with the governor and speaker of the House, had outsized influence on what became law.
For Rosenberg, it likely closes the final chapter of a lengthy legislative career during which he successfully solved some of Beacon Hill’s thorniest puzzles, from making resort-style casinos legal to redrawing the state’s legislative boundaries to overhauling the state’s criminal justice system.
Rosenberg, the first openly gay man to lead the Senate, also played a key role in plowing money into the University of Massachusetts system and in two major civil rights battles during his more than three decades at the State House: protecting gay marriage and passing a law that protects transgender people from discrimination in locker rooms, malls, libraries, restaurants, and other public accommodations.
“Stan was a critical leader in the fights for LGBT equality for the last three decades,” said Arline Isaacson, a veteran lobbyist and cochair of the Massachusetts Gay and Lesbian Political Caucus. “He was an absolute hero to our community, and he’s going to be sorely missed.”
Rosenberg has said Hefner’s presence in his life helped him become the person he is today, supporting him as he beat back cancer and giving him strength to disclose that he is gay.
“It was very difficult getting to this point in my life, frankly, to actually have relationships, and he actually brought me to the dance, if you will,’’ Rosenberg said in 2014. “I would not have come out if he had not come into my life. It was the greatest gift anyone has given to me.”
Both former foster children, the two became romantically involved in 2008 and married eight years later.
But Hefner, 30, was also a pernicious presence in Rosenberg’s life, the report found, repeatedly engaging in behavior that ranged from childish to criminal.
He texted pictures of nude men to Rosenberg, who “was angered by it because ‘a few times’ he accidentally opened a picture of a naked man from Hefner in a meeting and had to quickly hide his phone so other people would not see [the] picture,” the report found.
He posed as Rosenberg in electronic communications, using the senator’s phone to berate two staff members on July 4, 2016. Pretending to be their boss, he texted them that they were failures and then said: “Sometimes the best person for the job is a straight white man . . . . Or a whole office full.”
After the Globe story in November, Rosenberg stepped down as president, but remained a senator. His leave from leadership was meant to be temporary. But after the Globe reported in February that Hefner had access to Rosenberg’s e-mails, tried to affect the state budget, and involved himself in the workings of Rosenberg’s office, and in Senate affairs, senators foreclosed the possibility of him returning to the top legislative post.
Hefner was indicted in March. Rosenberg maintained that he had not known about Hefner’s alleged criminal acts, and the report found no evidence to contradict that claim.