Richard L. Armitage, who served as the No. 2 official at the State Department from 2001 to 2005, during the turbulent era of the 9/11 attacks and the start of America’s retaliatory wars in Afghanistan and Iraq, died on Sunday. He was 79.

The cause was a pulmonary embolism, Armitage International, a consulting company that Mr. Armitage ran in Arlington, Va., said in a statement. The statement did not say where he died.

Barrel-chested and with a shaved head, Mr. Armitage, a Naval Academy graduate who served in Vietnam, worked for three Republican presidents in senior foreign policy and defense jobs, part of a decades-spanning coterie of government officials who believed in a muscular American presence abroad.

He was one of a group, led by Condoleezza Rice, who called themselves “the Vulcans,” advising an inexperienced President George W. Bush on defense issues during his presidential campaign and first term.

Mr. Armitage, however, achieved unwelcome notoriety as the unnamed source of a 2003 news account that revealed the secret identity of a Central Intelligence Agency operative, Valerie Plame Wilson, shortly after the invasion of Iraq.

The Bush administration made the case for war based on exaggerated claims that Iraq was tied to the attacks of Sept. 11, 2001, and harbored weapons of mass destruction.

What came to be known as the “Valerie Plame affair” spun into a Washington scandal, with a full-court press by the news media and a criminal investigation by a special prosecutor.

Ms. Wilson was publicly named after her husband, Joseph C. Wilson IV, wrote an opinion column in The New York Times accusing President Bush of misleadingly claiming that Iraq had tried to buy uranium in Africa for nuclear weapons.

Mr. Wilson, a former state department official, accused the Bush administration of outing his wife in retaliation for his criticism.

A week after Mr. Wilson’s article was published, the conservative columnist Robert Novak revealed Ms. Wilson’s name, which was classified, setting off a special prosecutor’s investigation into the source of the leak.

Mr. Armitage, who cooperated with the investigation, publicly revealed three years later that he was the source. He said the disclosure was inadvertent, and he offered his apologies to former colleagues and to the Wilsons. No criminal charges were brought over the leak, although I. Lewis Libby Jr., an aide to Vice President Dick Cheney, was convicted of lying to investigators in 2007. (President Bush granted him clemency the next month.)

“It was a terrible error on my part,” Mr. Armitage said in an interview with The Times in 2006. “There wasn’t a day when I didn’t feel like I had let down the president, the secretary of state, my colleagues, my family and the Wilsons.”

Mr. Armitage’s tenure in senior roles in the State and Defense Departments began during the Reagan administration.

In the 2000 election, he and other members of the Vulcans — hawkish foreign policy insiders from earlier Republican presidencies — teamed up to advise Mr. Bush, who, as the governor of Texas, was new on the national stage.

Ms. Rice became President Bush’s national security adviser; Colin L. Powell became secretary of state; and Mr. Armitage, one of Mr. Powell’s best friends, was confirmed by the Senate as his deputy secretary.

Following the terrorist attacks of Sept. 11 — when the Vulcans, who also included Mr. Cheney and Defense Secretary Donald H. Rumsfeld, led the aggressive American response — Mr. Armitage spoke with a Pakistani general, seeking support in what would become the American-led war on terror.

The president of Pakistan, Pervez Musharraf, later told the CBS News program “60 Minutes” that Mr. Armitage had threatened to bomb his country “back to the Stone Age” if it didn’t support the United States. Mr. Armitage denied that he had threatened military action against Pakistan.

He offered his resignation from the State Department in November 2004, after President Bush’s re-election, and one day after Mr. Powell announced he was stepping down, fulfilling an agreement with the president that he would serve only four years as the nation’s chief diplomat. Mr. Armitage officially departed in February 2005 and entered the private sector.

In 2009, he said that the C.I.A.’s waterboarding of terrorism detainees, which the Bush White House had approved, was wrong and a form of torture.

“I hope, had I known about it at the time I was serving, I would’ve had the courage to resign,” he said in an interview with The Los Angeles Times. “But I don’t know. It’s in hindsight now.”

Richard Lee Armitage was born on April 26, 1945, in Wellesley, Mass., and grew up in Atlanta. He graduated from St. Pius X Catholic High School there in 1963.

Following his graduation from the Naval Academy in Annapolis, Md., he served on a destroyer off the coast of Vietnam. He then volunteered to serve as an adviser to Vietnamese forces, and he became conversant in Vietnamese during three tours with them. He earned a Bronze Star.

After the fall of Saigon in 1975, Mr. Armitage led a flotilla of 30,000 Vietnamese evacuees to safe harbor in the Philippines, according to a Naval Academy biography.

He entered government that year as a Pentagon consultant and later was an aide to Senator Bob Dole of Kansas.

Mr. Armitage was a foreign policy adviser to Ronald Reagan in the 1980 presidential campaign and then joined the Reagan administration as an assistant secretary of defense for East Asia and the Pacific. From 1983 to 1989, he was assistant secretary of defense for security policy.

Under President George H.W. Bush, he was an emissary to King Hussein of Jordan during the 1991 Persian Gulf war and an ambassador to East European states after the fall of the Soviet Union. He founded Armitage International after leaving government in 2005 and ran it until his death.

His survivors include his wife, Laura (Samford) Armitage; eight children; a brother and a sister; and 12 grandchildren. He and his wife were also foster parents of many children.

In the 2016 presidential election, Mr. Armitage endorsed Hillary Clinton over Donald J. Trump. Four years later, he was one of more than 130 former Republican national security officials who signed a statement calling Mr. Trump “dangerously unfit” to serve a second term. He endorsed Joseph R. Biden Jr. in the 2020 race.