The Massachusetts lawmaker has flown to Afghanistan and Pakistan numerous times to tamp down diplomatic disputes, spending hours drinking tea and taking walks with Afghan President Hamid Karzai or engaging in delicate negotiations in Islamabad.
It's a highly unusual role for a Senate Foreign Relations Committee chairman: envoy with a special but undefined portfolio.
Kerry has pushed the White House's national security agenda in the Senate with mixed results. He successfully ensured ratification of a nuclear arms reduction treaty in 2010 and most recently failed to persuade Republicans to back a U.N. pact on the rights of the disabled.
Throughout this past election year, he skewered Obama's Republican rival, Mitt Romney, at nearly every opportunity and was a vocal booster for the president's re-election. Kerry memorably told delegates at the Democratic National Convention in August: "Ask Osama bin Laden if he's better off now than he was four years ago."
Obama seems likely to reward all that work by nominating the 69-year-old Kerry, perhaps in the coming days, to succeed Secretary of State Hillary Rodham Clinton as the nation's top diplomat. The prospects for the five-term senator soared last week when U.N. Ambassador Susan Rice, a top contender for the post, withdrew from consideration to avoid a fierce fight with Senate Republicans.
A Kerry nomination has been discussed with congressional leaders, and consultations between the White House and congressional Democrats have centered on the fate of his Senate seat, according to officials familiar with the situation who were not authorized to publicly discuss the talks. If the seat were in play, it could boost the prospects for recently defeated Republican Sen. Scott Brown to win back a job in Washington.
At the same time, Obama is considering one of Kerry's former Senate colleagues, Republican Chuck Hagel of Nebraska, for the Pentagon's top job.
The selection of Kerry would close a political circle with Obama. In 2004, it was White House hopeful Kerry who asked a largely unknown Illinois state senator to deliver the keynote address at the Democratic convention in Boston, handing the national stage to Obama. Kerry lost that election to President George W. Bush. Four years later, Obama was the White House hopeful who succeeded where Kerry had failed.
Senate colleagues in both parties say Kerry's confirmation would be swift and near certain, another remarkable turnaround. Eight years ago, the GOP ridiculed Kerry as a wind-surfing flip-flopper as he tried and failed to unseat Bush.
"If he is nominated, he comes into the position with a world of knowledge. He's someone who certainly understands how the legislative process works, and I think he will be someone that Congress will want to work with in a very positive way," said Sen. Bob Corker of Tennessee, who is poised to become the top Republican on the Foreign Relations Committee next year.
Sen. Kelly Ayotte, R-N.H., a member of the Senate Armed Services Committee, said "there's no question he has a very strong depth of knowledge of these issues. Certainly qualified."
Sen. John McCain, R-Ariz., has taken to jokingly referring to Kerry as "Mr. Secretary."
Kerry and McCain, defeated presidential candidates who returned to the Senate, have joined forces repeatedly during the past few decades. In July 1995, the two decorated Vietnam War veterans provided political cover to President Bill Clinton when he normalized U.S. relations with Vietnam. Clinton had been dogged by questions about his lack of military service.
Last year, Kerry and McCain were outspoken in pushing for a no-fly zone over Libya as Moammar Gadhafi's forces attacked rebels and citizens. This month, they stood together in arguing for the disabilities treaty against staunch Republican opposition and complaints that it could undermine U.S. national sovereignty.
The pact fell five votes short of ratification, and Kerry called it "one of the saddest days I've seen" in his years in the Senate.
"Today I understand better than ever before why Americans have such disdain for Congress and just how much must happen to fix the Senate so we can act on the real interests of our country," he said, his frustration evident.
Kerry has traveled extensively for the administration, to Afghanistan in May as a strategic partnership agreement loomed large in the decade-plus war. He was in Pakistan last year in the midst of a diplomatic crisis after Raymond Davis, a CIA-contracted American spy, was accused of killing two Pakistanis.
Sen. Chris Coons, D-Del., a member of the Foreign Relations Committee, traveled to Pakistan around that time and recalled Kerry's influence.
"I arrived in Islamabad I think five days after Ray Davis had been taken into a jail in the Punjab and was at very real risk of being hauled out of the jail and lynched," Coons said. "Sen. Kerry was about to show up and negotiate on behalf of the administration. And it was clear that both the diplomats and the military folks we met with viewed him as a real man of credibility and experience who was likely to contribute meaningfully to those negotiations."
Davis pleaded self-defense. After weeks of wrangling between the U.S. and Pakistan, he was released in exchange for "blood money" paid to the dead men's relatives.
This year, Kerry has presided over committee hearings on treaties and other major issues, but there has been little legislative work. He didn't draw much attention to the committee, avoiding possible embarrassments for the administration in an election year.
Corker said he would have liked for the committee to devote more time to events in Libya, Syria and other countries.
"I think he's tried to accommodate our concerns and at the same time seek a balance ... giving the administration the headroom they needed to do what he and the administration felt was best. I understand that," he said, speaking of Kerry.
Coons said Kerry's deliberate work is often behind the scenes.
"The role of the chairman ... is not always getting your picture taken with George Clooney, standing around with heads of state, going to receptions in Foggy Bottom," he said. "It's also lots and lots of time listening to folks who've got concerns whether it's on behalf of the defense community, the business community, the diplomatic community and being the person who's at the intersection of all that and trying to keep the Senate productively engaged in a very dangerous world with a lot of emerging threats."
Associated Press writer Steve Peoples in Boston contributed to this report.
Donna Cassata can be reached on Twitter at http://twitter.com/DonnaCassataAP