Facing growing business pressures, The Washington Post shook up its newsroom on Tuesday by naming Boston Globe editor Martin Baron as its new executive editor, replacing Marcus Brauchli, who had held the job since 2008.

Baron, 58, is only the fourth journalist appointed to the job in the past 44 years and the second outsider named to run the paper’s editorial operations during the past four.

Brauchli, 51, led the newsroom during a particularly challenging financial period for the news industry. He is officially resigning, but his tenure has been marked recently by tension with Post Publisher Katharine Weymouth, especially over budget and financial issues.

Baron has been editor of the Globe since 2001. He will assume the top editorial position at The Post on Jan. 2.

Weymouth, Brauchli and Donald Graham, chief executive of The Washington Post Co., were reluctant to discuss the circumstances surrounding Brauchli’s departure as executive editor in interviews Tuesday. Brauchli was Weymouth’s choice for the job four years ago; he was chosen to run The Post’s newsroom several months after he was forced to resign as editor of the Wall Street Journal following its purchase by Rupert Murdoch’s News Corp.

Marcus Brauchli, executive editor of the Washington Post, will step down at the end of the year. (BILL O'LEARY/THE WASHINGTON POST)

Weymouth said in an interview that Brauchli “decided to step down.” But she acknowledged, “In this day and age, there’s always some tension between the publisher and the editor. Did we always see eye to eye? Of course not. But we had a strong enough relationship to talk through our differences.”

Brauchli, who will become a vice president of The Washington Post Co. with responsibility for evaluating new media opportunities, said, “It made sense to make a change at this time, and Don had an interesting job that he wanted done.” Brauchli said that he and Weymouth “mutually agreed” to his resignation.

Hours before the announcement, Brauchli had issued a rare stop-the-presses order early Tuesday to get late-breaking news about the unfolding scandal around former CIA director David H. Petraeus into late copies of the paper.

Weymouth, Brauchli and Graham jointly announced the transition to The Post’s newsroom Tuesday morning. While the change of editors had been rumored for several months, there were many expressions of surprise among staff members that it had actually taken place.

Brauchli recounted some of the journalistic highlights of his eventful tenure in remarks to the paper’s journalists, coverage of two wars, the Arab Spring, weather calamities and last week’s election among them. His comments were followed by about 60 seconds of applause. Brauchli was visibly moved by the reception.

During the meeting, Weymouth was asked just one question by a Post reporter: “Why did you do this?” She declined to answer.

The announcement represents an uncharacteristic bit of turbulence for a newsroom that was guided for decades by just two men, Benjamin C. Bradlee and his successor, Leonard Downie Jr., who spent his entire journalism career at the paper. Brauchli was the first non-Post employee in decades to assume the top newsroom position when Weymouth hired him in July 2008.

The transition also reflects nearly wholesale change at the top of The Post. In addition to Brauchli, Managing Editor Liz Spayd had previously announced that she would be leaving after the election. (She will stay on until the end of January to help smooth the editor transition.)

After Brauchli and Spayd, the most senior newsroom executive is Managing Editor John Temple, who joined the paper at the end of April.

Although The Post’s Web site is drawing record numbers of visitors, the traditional newspaper has been under stress from a prolonged shift away from lucrative print advertising to cheaper and less-profitable digital advertising.

At the same time, readers have gradually abandoned the printed paper for digital alternatives, putting continued financial pressure on newsrooms everywhere. The Post’s daily and Sunday circulation have declined 20.5 percent and 19 percent, respectively, over the past four years, according to the Audit Bureau of Circulations.

This led to cost-cutting pressure, as well as to a search for new sources of revenue. Among the most successful was the launch of Washington Post Live, which puts on conferences and panels that host live discussions about topics in the news. Those events succeeded an embarrassing — and quickly discarded — plan led by Weymouth to hold private sponsored “salons” with government officials and lobbyists at Weymouth’s home.

Senior executives in the newsroom were recently at odds with the newspaper’s business side, led by President and General Manager Steve Hills, over what the newsroom saw as insufficient initiative in generating additional revenue. Weymouth was caught in the middle, moderating between factions.

Before becoming editor of the Globe, Baron held senior editing positions at the New York Times, the Los Angeles Times and the Miami Herald. The Globe, which is owned by the New York Times Co., has won six Pulitzer Prizes during his tenure, including those for public service, explanatory journalism, national reporting and criticism.

“The Washington Post has played a defining and inspirational role in American journalism, and today it continues to lead as our profession undergoes a dramatic, urgent, and exciting transformation,” Baron said. “I am honored to join the supremely talented and dedicated journalists at The Washington Post.”

Baron has also faced financial issues at the Globe, and is generally admired within the industry for his efforts to manage his newsroom’s costs. But Weymouth said of him: “I’m not bringing in Marty to make cuts. I’m bringing him in because he’s a great editor. He’s coming to do great journalism.”

Baron is both a well-liked and well-connected figure within the business after having worked at several of the nation’s top papers.

“He has a wonderful chuckle and dry sense of humor,” said Jill Abramson, the editor of the New York Times. “He also has a news gut that is close to perfect pitch. Both are incredibly galvanizing to reporters during long and stressful chases. He’s managed to trim his staff without trimming the ambitions of the journalism he produces. I imagine this will be a challenge at The Post, but it’s one where he has proven success.”

When Baron was executive editor of the Herald, it won the Pulitzer Prize for breaking-news coverage in 2001 for its reporting on the federal raid that recovered Elián González, the Cuban boy at the center of a fierce immigration and custody dispute. Baron was named editor of the year by Editor & Publisher magazine in April 2001, and he was selected by the National Press Foundation as editor of the year in 2004.

He began his career at the Herald in 1976 and moved to the Los Angeles Times in 1979, moving up the masthead as business editor and as assistant managing editor for page-one special reports, public opinion polling and special projects. He later became editor of the paper’s largest regional edition, in Orange County, which then had about 165 staffers.

Baron joined the New York Times in 1996 and in 1997 became associate managing editor responsible for its nighttime news operations.

During Brauchli’s four-plus years at The Post, the newsroom won four Pulitzer Prizes and was a finalist for eight others. It also won a variety of other awards, including a George Polk and a Peabody award. It also beefed up its Web site and launched a series of digital initiatives.

The newsroom did so while the newspaper’s budget shrank by about 30 percent, according to senior editors, and the newsroom’s staff fell as a result of a series of buyouts.

“Marcus led us through the most dramatic remaking of the newsroom that this place has ever seen,” said Spayd, the managing editor. “We were immersed in a print-centric culture when he arrived and Marcus planted us firmly in the 21st century, with relatively minimal pain. Marcus has the qualities I admire most in a boss: He’s a brilliant journalist, and he’s a kind, humane leader. He’ll be missed.”