John Kerry is the son of a US diplomat, who grew up among the rubble of Berlin, criss-crossed Europe as a child, fought in Vietnam, has met many world leaders and negotiated tough deals for America.

And in just a few days the veteran senator, who has diplomacy sewn into his DNA, is set to land his dream job, taking the helm of the State Department and its 70,000 employees, and helping shape America's future foreign policy.

He has big shoes to fill. Hillary Clinton, the former first lady and ex-New York senator, has won accolades and the expansive title of "the rock star diplomat" during her four years on the job.

For the past few weeks, Kerry has been quietly, unobtrusively, doing the rounds at the State Department being briefed on the intractable dossiers about to hit his in-tray, meeting the staff, evaluating the contours of his new team.

In nominating Kerry last month to be the next secretary of state, President Barack Obama said of the long-time member of the Senate Foreign Relations committee: "He is not going to need a lot of on-the-job training."

"It's as if John Kerry stepped out of one of those portraits on the seventh floor of the State Department. He's been in training for this job for decades," said Martin Indyk, director for foreign policy, at the Brookings Institution.

But Indyk predicted a change of style, under the leadership of the 69-year-old Kerry, if he is confirmed by the US Senate as expected on Tuesday.

"He'll, I think, want to be much more engaged in the nitty-gritty of negotiations where that becomes possible," he said on the think-tank's website.

"Hillary Clinton has done a fantastic job of rebuilding America's images and standing in the world, and Secretary of State Kerry, if he is confirmed, will have the opportunity to work off that platform in trying to help shape the emerging global order for the president."

At his confirmation hearing on Thursday, Kerry turned to some of the biggest issues facing the United States today.

He warned Iran the US would do "what we must" to stop it from getting a nuclear weapon, told China he would work to strengthen ties and hinted at a "way forward" in the Middle East peace process.

Already, the Israeli Haaretz newspaper quoting senior Israeli officials said Kerry was planning an early visit to both Israel and the Palestinian territories in February.

By comparison Clinton during her tenure made only five trips to Israel, and two to the Palestinian Authority as the Middle East peace process was left on a back-burner after Obama tried and failed to bring the two sides together.

As the US withdraws its troops from Afghanistan, Kerry, who knows President Hamid Karzai well, could also play a key role in determining the two nation's future relations.

Kerry also vowed to be "a passionate advocate" to tackle climate change, and talked about the need to combat the evolving threat posed by Al-Qaeda.

"We cannot afford a diplomacy that is defined by troops or drones or confrontation," the Vietnam veteran told US lawmakers.

"We need to be sort of thoughtful about the history and the culture and the nature of the places that we're dealing with. And you can't just take an American concept and plunk it down or a Western concept and plunk it down and say, this is going to work."

After fighting in Vietnam, Kerry became a vociferous anti-war campaigner on his return. Famously, he testified before the Senate Foreign Relations Committee in 1971 about the Vietnam War asking: "How do you ask a man to be the last man to die for a mistake?"

"If there is such a thing as a Kerry Doctrine, it is a clear-eyed willingness to pursue engagement and test the intentions of other countries, even present and former enemies or difficult partners on the world stage," says Douglas Brinkley, professor of history at Rice University, in the online magazine Foreign Policy.

"Kerry exudes noblesse oblige. But his courtesy and diplomatic finesse can mask a toughness and a willingness to speak hard truths," he wrote.

His deeply-held instinct not to rush to intervene also wins fans.

"There's a combination of prudence and knowledge," Christopher Preble, vice president for foreign policy studies at the Cato Institute, told AFP.

"I think he'd be somewhat less enthusiastic about the United States becoming involved in a Syria or something like that."

Privately, some among the foreign service are happy to be welcoming back one of their own, and while Clinton has been a popular boss the added personal political spotlight surrounding her has at times been seen as a distraction.

But Aaron David Miller, former advisor to six secretaries of state, said only time would tell if Kerry would become "a consequential" secretary of state reaching the halls of fame like Henry Kissinger.

"A lot of being a great secretary of state is luck. Right time, right place," he told AFP.

"You need a set of negotiating skills, I call it the negotiator's mindset in which you can intuit the deal," Miller said. "You need serendipity... you need an opportunity that allows you the chance to open the door."