To mark the 20th anniversary of the American-led invasion of Iraq, the C.I.A. director, William J. Burns, stood in the lobby of the agency’s headquarters in Langley, Va., and sought to exorcise the ghosts of the prewar intelligence failures that haunt the building to this day.

Addressing some 100 C.I.A. officials on March 19, Mr. Burns acknowledged how the agency catastrophically blundered in its assessment that Iraq had weapons of mass destruction. But he noted, according to two people present, that there was ample blame to go around. The culprits included a hubris-stricken Bush White House as well as the State Department — where Mr. Burns served at the time as a senior official — which he said had unwarranted confidence that it could derail the invasion plans.

Notably Mr. Burns added, “We’ve learned from that hard lesson.” The intelligence the agency and others collected on Russia’s plans to invade Ukraine, he said, “stands as a powerful example of that. It enabled us to provide strong, resolute and confident warning, to help the Ukrainians defend themselves and to help the president cement a strong coalition.”

The tableau was a reminder that Mr. Burns, 67, has for decades been a near-omnipresent if subdued actor on the American foreign policy stage, having served every Democratic and Republican president since Ronald Reagan, with the exception of Donald J. Trump. And yet the moment only hinted at how Mr. Burns, a key figure in the Biden administration’s support of Ukraine, has amassed influence beyond most if not all previous C.I.A. directors.

His ascent is an unlikely turn for a tall, discreet figure with wary eyes, ashen hair and a trim mustache, a sort you could easily imagine in a John Le Carre novel whispering into a dignitary’s ear at an embassy party that the city is falling to the rebels and a boat will be waiting in the harbor at midnight.

The impact of his two-year tenure has been as sweeping as it has been subtle. The C.I.A., demoralized and marginalized during the Trump years by a president who said publicly that he believed Mr. Putin over his own intelligence agencies, has entered a period of resurgent prestige. As a member of Mr. Biden’s inner circle who once served as the ambassador to Russia, Mr. Burns has helped restore America’s upper hand over Mr. Putin. Though spy chiefs are typically relegated to the shadows, the Biden administration has thrust theirs into the spotlight.

It was Mr. Burns, rather than Secretary of State Antony J. Blinken, whom Mr. Biden dispatched in November 2021 to Moscow, where from a Kremlin phone the C.I.A. director spoke with Mr. Putin (who was in Sochi that day) for an hour and warned him not to invade Ukraine. Three months earlier, Mr. Burns was in Kabul to meet with Taliban leaders and thus confer legitimacy on the regime as the United States was withdrawing troops from Afghanistan.

Mr. Burns, who declined to be interviewed on the record for this article, has also taken some three dozen trips overseas during his two years as director, often to meet with agency section chiefs and their foreign counterparts, as is customary, but also to discuss U.S. policy with foreign leaders in Egypt, Libya and elsewhere. Mr. Biden frequently asks Mr. Burns to accompany the regular C.I.A. briefer to the Oval Office for the president’s daily national security briefing, when the president sometimes solicits and gets Mr. Burns’s opinions on policy matters, an administration official said.

Previous C.I.A. directors have played a role in U.S. foreign policy — George Tenet was harshly criticized for tailoring intelligence to justify the 2003 invasion of Iraq and served as an interlocutor in peace negotiations between Israel and the Palestinians — but the position has traditionally been viewed as an objective overseer of intelligence gathering separated from policy and political influence.

Mr. Burns, however, is the first C.I.A. director to have previously been a career diplomat (for 32 years), and is on a first-name basis with numerous foreign leaders. He speaks Russian, French and Arabic. “He’s one guy you weren’t bringing in and having to break out a map for, or having to explain why it is that the Turks don’t like the Kurds,” said Eric Traupe, who until last summer was the C.I.A.’s assistant director for the Near East.

Mr. Burns, Mr. Traupe said, is relied upon as an in-house resource for the administration, including by Mr. Blinken and Jake Sullivan, the national security adviser, on how to deal with foreign adversaries. It’s “what’s he like, how do you negotiate with him?” said Mr. Traupe, who praised Mr. Burns’s deftness so far in “not being the center of attention.”

Of course, the absence of drama in the Biden foreign policy team can also produce “groupthink,” said Douglas London, a former C.I.A. clandestine services officer who later served as a counterterrorism adviser for the Biden campaign and is now an author and professor at Georgetown University.

As an example, he cited the administration’s failure to foresee the swift collapse of the Afghan military as U.S. troops withdrew from the country in August 2021. Though Mr. Burns has publicly maintained that the C.I.A.’s assessments of the Afghan military’s resolve were “on the pessimistic end of the scale,” the director of national intelligence, Avril D. Haines, acknowledged after the collapse that it “unfolded more quickly than we anticipated, including in the intelligence community.”

The son of a two-star Army general who fought in Vietnam, Mr. Burns attended La Salle University in Philadelphia, then won a scholarship to the University of Oxford, where he developed his appetite for international relations. He met his future wife, Lisa Carty, in 1982, when the two were seated alphabetically next to each other during foreign service orientation. (Ms. Carty now serves as the ambassador to the United Nations Economic and Social Council.)

Mr. Burns and Mr. Biden go back roughly a quarter-century, when Mr. Burns was the U.S. ambassador to Jordan and Mr. Biden was the senior Democrat on the Senate Foreign Relations Committee. They grew closer during the Obama years, when Mr. Burns was the deputy secretary of state and Mr. Biden was vice president. In national security discussions, Mr. Biden and Mr. Burns agreed on not aggressively pushing President Hosni Mubarak of Egypt to step down during the Arab Spring in 2011, but they diverged on conducting airstrikes on the Qaddafi regime in Libya and on raiding the compound in Abbottabad, Pakistan, where Osama bin Laden took refuge. In both cases Mr. Biden urged restraint and Mr. Burns urged action.

As Mr. Burns prepared to step down from government service in 2014, The Wall Street Journal reported last month, a mutual friend introduced him to Jeffrey Epstein, the financial consultant who would later be convicted of multiple sex crimes. A spokeswoman for the C.I.A. said that Mr. Burns met twice with Mr. Epstein, both times to discuss private sector opportunities, and did not socialize with him.

In a statement to The New York Times, Mr. Burns said that he deeply regrets having met with Mr. Epstein and did not know who he was, adding, “I wish I had done my homework first.”

After Mr. Biden won the presidency in 2020, transition officials asked Mr. Burns if he was interested in an ambassadorship to Japan or China, according to two people familiar with the dialogue. But before Mr. Burns could respond, Mr. Biden’s preferred candidate for C.I.A. director, Thomas E. Donilon, a former Obama national security adviser, decided against taking the job. Mr. Biden then focused on Mr. Burns, who had never aligned himself with any partisan cause and thus would not face a difficult path to confirmation. He was ultimately confirmed in the Senate by a voice vote.

Mr. Burns inherited an agency reeling from Mr. Trump’s open disdain of the intelligence community, not to mention the lingering aftershocks of two wars and a terrorist attack on U.S. soil. Mr. Trump’s first C.I.A. director, Mike Pompeo, had come into office with a conservative agenda and in an early meeting, according to a witness, accused senior analysts of “already having made your minds up” before producing an assessment that Russia had tried to help elect Mr. Trump in 2016.

Mr. Pompeo’s replacement, Gina Haspel, a career case officer, made a more conscious effort to insulate the agency from Mr. Trump’s whims, former officials said, but at times her efforts to mollify him struck some in the agency as unseemly. That included when she publicly praised Mr. Trump’s “wisdom” in engaging with North Korea in 2019 and when she stood and applauded the president during his State of the Union address a year later.

All of which is to say that Mr. Burns had a low bar to clear upon taking office in March 2021. Current and former members of the intelligence community praise him for some internal changes, including working to stabilize the agency, pressing for greater diversity in the work force and instituting a mission center devoted to employee wellness.

Externally there have been more tangible successes, most notably the intelligence sharing with Ukraine that is widely credited with improving Kyiv’s ability to anticipate maneuvers by Russia’s military. An additional source of support for Ukraine has been the selective declassification of intelligence documents to expose Russian disinformation, which grew out of discussions between Mr. Burns, Mr. Sullivan and Ms. Haines, after Ms. Haines’s office formalized a system to avoid revealing sources and methods in the process.

By contrast, the C.I.A. under Mr. Burns has shown restraint on the origin of the coronavirus. In February new intelligence prompted the Energy Department to conclude that the virus had most likely been accidentally leaked from a laboratory in Wuhan, China. But the department did so with “low confidence,” and the C.I.A. remains unpersuaded, according to two people familiar with the process. The C.I.A. has so far declined to issue its own conclusion.

In the meantime Mr. Burns has called China America’s foremost adversary, one whose influence pervades nearly every aspect of the agency’s intelligence-gathering mission, from military capability to digital influence to mineral resource acquisition. As a result, the director has moved the C.I.A.’s disparate China-related departments into a single mission center. Doing so — along with his increasing promotion of the agency’s efforts to address the flood of fentanyl across the U.S.-Mexico border — dovetails with Mr. Biden’s political agenda as the president heads into a bruising re-election campaign.

Should the president win a second term, people close to the administration speculate that Mr. Burns would be a candidate to replace Mr. Blinken, should Mr. Blinken choose to step down. Mr. Burns refuses to talk about it, as do his colleagues. Richard Armitage, Mr. Burns’s friend and former superior at the State Department, said only, “Whatever the president asks, he’ll do it.”