As expected, President Barack Obama nominated Sen. John Kerry on Friday to succeed Hillary Rodham Clinton as secretary of State.

“John’s earned the respect and confidence of leaders around the world,” Obama said Friday in announcing his pick. “He’s not going to need a lot of on-the-job training.”

For the Massachusetts Democrat, who chairs the Foreign Relations Committee, the decision is the culmination of a long-held ambition to helm the nation’s foreign policy from the executive branch.

Kerry’s confirmation is all but assured. Many Republicans had pre-endorsed him for the job and had taken to calling him “Mr. Secretary” in recent weeks, particularly after fierce Republican opposition led United Nations Ambassador Susan E. Rice to take herself out of the running for the post. A swift confirmation is expected early next year.

On Friday, Sen. Lindsey Graham, R-S.C., called Kerry “a very solid choice by the president.” And Sen. John McCain, R-Ariz., said he has “confidence in his ability to carry out that job.”

Several other Republicans also suggested Kerry would not face concerted opposition.

“I think a lot of us could support him,” Sen. Richard C. Shelby, R-Ala., said Friday. “He’s been involved in this a long time; he’s very mature now, like a lot of us.”

Bob Corker, R-Tenn., likely the next ranking member on the Senate Foreign Relations Committee, would not comment Friday on whether he would vote to confirm Kerry.

But Corker said, “I do think he’ll be easily confirmed.”

“Sen. Kerry and I had a good working relationship on Foreign Relations,” Republican Sen. Marco Rubio of Florida said Friday. “Obviously we have disagreements on some foreign policy issues and on many domestic ones, but he has always been respectful of my views and has always given me the opportunity to air them. He’s clearly qualified.”

Rubio added that Kerry will, like any nominee, have to go through the Senate vetting process. But, given Kerry’s well-known record as a senator and presidential nominee, Rubio said he doesn’t expect any surprises.

The pick of Kerry sets the stage for a special election battle in Massachusetts, where defeated Republican Sen. Scott P. Brown is expected to try to return to the Senate.

Kerry’s impending departure leaves an opening atop the Foreign Relations Committee. Sen. Robert Menendez, D-N.J., is widely expected to succeed Kerry as chairman. Menendez’s ascension is likely to lead to a more combative relationship between the Senate and the White House on several areas of foreign policy, particularly toward Cuba and Iran.

Kerry would bring deep experience in foreign affairs to the State Department post.

Even before he was elected to the Senate in 1984, Kerry, a Navy veteran who rose to the rank of lieutenant, was prominent in protesting the war in Vietnam.

Later, he was an outspoken critic of the Iraq war, particularly during his unsuccessful presidential bid in 2004.

Since becoming chairman of Foreign Relations in 2009, Kerry has been particularly visible on issues surrounding the war in Afghanistan and the U.S. relationship with Pakistan. He was instrumental in putting together an ambitious aid package (PL 111-73) in 2009 that authorized $7.5 billion in civilian aid over five years. Congress has appropriated the money for the past three years.

But he has also been a skeptic of the large-scale plans, first in Iraq and later in Afghanistan, for civilian aid and reconstruction programs. As secretary of State, he would be in charge of determining how to manage the U.S. role in Afghanistan amid a drawdown aimed at ending the U.S. combat presence by the end of 2014.

Megan Scully contributed to this report.