Last summer, as many one-time adversaries of President Trump sought to bury the hatchet with him, he met with someone who seemed like a intractable enemy: his former personal lawyer and fixer, Michael D. Cohen.

Mr. Cohen and Mr. Trump had a brief yet significant conversation at the president’s private, members-only golf club in Bedminster, N.J., breaking a yearslong estrangement marked by legal disputes and public acrimony, according to people with knowledge of the encounter, who discussed the private session on the condition of anonymity.

Their conversation, which has not been previously reported, provided Mr. Cohen a toehold into Mr. Trump’s orbit and set in motion a broader effort to make peace with the president. His private outreach also included a second, longer meeting with Mr. Trump this year and calls to some of the president’s closest allies.

Mr. Cohen’s public stance has shifted as well. Two years after serving as the star witness against Mr. Trump at the president’s criminal trial in New York — delivering testimony that helped secure his conviction for falsifying business records — Mr. Cohen has publicly assailed the prosecutors leading the case.

In an interview on Saturday, Mr. Cohen said his relationship with the president had improved in recent months after Mr. Trump had noticed a liberal backlash to his criticism of prosecutors.

“If Donald Trump and Michael Cohen can rekindle and reconcile their past relationship, then anyone should be able to,” he said.

Mr. Cohen stands to gain from the rapprochement. With the White House’s apparent blessing, he is debuting a radio show on Sunday on a Trump-friendly station in New York, WABC. He is filling former Gov. Andrew Cuomo’s slot during the summer, but he has said that he hopes to get a syndicated show eventually.

Unlike several prominent Trump critics who have legally sparred with the president, Mr. Cohen has not faced prosecution from Mr. Trump’s Justice Department, which has sought to bring charges against figures such as former F.B.I. director James Comey and New York attorney general Letitia James. Mr. Trump has not publicly attacked Mr. Cohen since retaking office.

The White House did not respond to requests for comment.

The truce represents a surprising third act in the tumultuous Trump-Cohen relationship.

The two men, both known for their tough-guy personas and tendency to lash out at enemies, have worked together, betrayed each other and now might soon be chatting again in public: While promoting his new show, Mr. Cohen recently said that he expected Mr. Trump to call in as a guest in the coming weeks.

On his show, Mr. Cohen could continue to undermine his role as a witness at Mr. Trump’s criminal trial, if his most recent public remarks are any indication.

During the Manhattan district attorney’s investigation into Mr. Trump over a hush-money deal with a porn actress, Mr. Cohen said he was helping prosecutors because Mr. Trump “needs to be held accountable for his dirty deeds.” Mr. Cohen, who went to prison for his role in the hush-money deal, now contends that he “felt compelled and coerced to deliver what they were seeking.”

Mr. Trump — who has recently told aides and confidants that he felt sorry for his former fixer, lamenting his time in prison — could try to leverage Mr. Cohen’s recent criticism of prosecutors as he challenges the legal cases against him. His lawyers have already cited Mr. Cohen’s comments in court papers, part of a broader effort by the president to recast the past decade, including his refusal to acknowledge his loss in the 2020 election.

There is also potential peril in Mr. Cohen and Mr. Trump’s reconciliation. Mr. Cohen may not stick to Trump’s talking points, having already noted publicly that he does not agree with the president on everything.

The two-decadlong relationship between them was born from conflicts, one involving New York real estate, rather than presidential politics. After buying apartments in two of Mr. Trump’s New York buildings, Mr. Cohen caught Mr. Trump’s eye during a dispute with the condo board at Trump World Tower in New York in the mid-2000s.

Mr. Cohen, who had idolized Mr. Trump since his youth on Long Island, saw a potential mentor and patron. Mr. Trump saw a potential bulldog enforcer.

Mr. Cohen often delivered. He threatened Mr. Trump’s foes — Mr. Cohen once wrote that he served as Mr. Trump’s “designated thug” — and occasionally worked on real estate projects.

Mr. Cohen was not given a formal role in the 2016 campaign. But he found ways to be useful to the president politically.

During the 2016 presidential campaign, Mr. Cohen played a pivotal role in covering up a potential scandal that could have damaged Mr. Trump’s candidacy. When the porn actress Stormy Daniels threatened to go public with her story of a sexual encounter with Mr. Trump, Mr. Cohen bought her silence with a $130,000 payoff.

In 2018, Mr. Cohen pleaded guilty to several federal crimes, including for his role in the payoff, though he said Mr. Trump had directed him to make the secret payment.

Mr. Cohen was the only person to serve prison time for that deal. Released during the pandemic, the Trump administration threw him back behind bars when he would not sign papers ruling out writing a book. A judge ordered him released, saying the move was “retaliatory.”

Mr. Cohen emerged from prison angry, saying he was determined to set the record straight. He released books titled “Disloyal” and “Revenge,” as well as a podcast called “Mea Culpa.” He also met with the Manhattan district attorney’s office, which ultimately indicted Mr. Trump for his role in the hush-money deal.

Mr. Cohen took the witness stand in that case. He also testified in a civil case that Ms. James brought against Mr. Trump, who was found liable for fraud.

Mr. Trump called Mr. Cohen a “rat” and a “liar.” He even sued Mr. Cohen, ultimately dropping the case days before Mr. Trump was set to be deposed.

For years, Mr. Cohen did not back down. In social media and on cable news, he boasted of his role in holding Mr. Trump accountable, noting that he had voluntarily testified before Congress and met with prosecutors some 20 times. He likened Mr. Trump to a mobster.

“If the country won’t forgive me, how can I ever forgive myself?” he wrote on Twitter in 2021. “It’s why I have and will continue to cooperate with law enforcement; to ensure Trump and company are held responsible.”

Mr. Cohen nevertheless has said he had some misgivings about testifying at Mr. Trump’s criminal trial. And some of Mr. Cohen’s friends have contended that he never wanted to break up with Mr. Trump and would have preferred remaining in his orbit, rather than enduring years of testimony and receiving accolades as a hero of the left.

After Mr. Trump returned to office last year, Mr. Cohen began to seek out his former boss.

His effort gained traction last summer, when he met with Mr. Trump at Bedminster. Mr. Trump’s top personal legal adviser, Boris Epshteyn, was present for the conversation but did not arrange it, the people briefed on the matter said.

It is unclear who did; Mr. Cohen has declined to say, and a White House spokesman did not respond to multiple requests for comment. The president and his aides have yet to comment on Mr. Cohen’s change in tone publicly.

Still, according to the people briefed on the initial Bedminster conversation, it broke the ice, without cementing a new relationship. By late summer, Mr. Cohen began softening his tone about Mr. Trump in television appearances.

In January, Mr. Cohen made a vocal public turn: In a Substack essay, he argued that he was an involuntary participant in the cases against Mr. Trump, compelled to testify by subpoena. He also accused prosecutors of posing “inappropriate leading questions to elicit answers that supported their narrative.”

Mr. Cohen has said he received a swift and furious reaction from liberal readers. That’s when a Trump associate brought the backlash to the president’s attention, Mr. Cohen recently said when he appeared as a guest on a WABC radio show. The associate, Mr. Cohen added, relayed to him that the president had expressed sympathy for him.

So, Mr. Cohen said, he texted the president to thank him and express “my sincere hope that this long, exhausting feud could finally end.” Mr. Trump responded, Mr. Cohen said. According to people with knowledge of the matter, they met in Florida some time after the Substack essay. It all unfolded “about six, seven months ago,” Mr. Cohen said in the appearance.

“We rekindled our relationship because of a shared experience of betrayal,” he said.

Mr. Cohen also contacted a number of Trump allies, including one of his lawyers and his daughter-in-law, Lara Trump, who then had him on her podcast. There, he defended Mr. Trump from questions about past ties to the sex offender Jeffrey Epstein.

Eventually, he landed on WABC, a home to Trump acolytes including Roger Stone.

John Catsimatidis, the station’s owner and a longtime Trump supporter, told The New York Post that he had checked with the White House before giving Mr. Cohen the show. In a brief call with The New York Times, he declined to elaborate.