Shriver has been residing apart from the actor-turned-politician for the last few weeks. The former first couple confirmed the separation in a joint statement released Monday after questions from The Times.
"This has been a time of great personal and professional transition for each of us," the statement read. "After a great deal of thought, reflection, discussion and prayer, we came to this decision together. At this time, we are living apart while we work on the future of our relationship.
Photos: A political marriage with star power
"We are continuing to parent our four children together. They are the light and the center of both of our lives. We consider this a private matter and neither we nor any of our friends or family will have further comment. We ask for compassion and respect from the media and the public."
Over the years, the marriage between the international celebrity and the daughter of the Kennedy dynasty has come under close scrutiny, especially during the 2003 recall of Gov. Gray Davis, when The Times reported on Schwarzenegger's lengthy history of groping women. At the time, Shriver defended her husband, helping lift him to victory in the free-for-all contest.
Since Schwarzenegger left office, it had seemed as though the two were living separate lives. Shriver, a former contributing anchor on NBC's "Dateline," has worked on her women's empowerment website, guest edited an issue of Oprah Winfrey's magazine and promoted causes near to her heart, such as Alzheimer's research. She struggled with the death of her father, Sargent Shriver, in January, and took her son Patrick and some of his friends on an East Coast college tour in April.
Shriver, 55, spoke openly about the uncertainty she felt about moving on to the next phase of her life. "It is so stressful to not know what you're doing next," Shriver said in a March 28 YouTube video to supporters. Though there was no intimation of a split, Shriver appeared without her wedding ring. "I'd like to hear from other people in transition," Shriver said. "How did you get through it? What were three things that enabled you to get through your transition?"
The former governor, 63, told a Times reporter in April that he yearned for a show business comeback. It was later announced that Schwarzenegger had signed on to star in three films, including another installment in the "Terminator" series.
"The whole industry has not come up with a new line of action heroes so [people say] let's go see the mature ones -- that's what I call them, the mature ones -- because there's nothing new around," Schwarzenegger said in the interview. "That's good news for me."
The couple met in 1977, when NBC's Tom Brokaw introduced Shriver to Schwarzenegger at a charity tennis tournament. The two married in 1986, and have four children, ages 14, 18, 20 and 21. Their marriage united Republican Schwarzenegger with Shriver, the daughter of the late Eunice Kennedy Shriver.
Their odd-couple political match was a source of endless interest to outsiders, and good-natured ribbing on the part of the couple, who often found themselves on opposites sides of political campaigns. In 2008, Shriver delivered a high-profile endorsement of Barack Obama on the eve of the California primary. Schwarzenegger backed the GOP nominee, Arizona Sen. John McCain.
Schwarzenegger was immensely popular in his first year in office, animated by dramatic Hollywood-style campaigning. But he left office last January sobered by years of budget difficulties and suffering from a fractious relationship with legislators from both parties.
Shriver emerged as perhaps the most prominent and powerful first lady in California history, promoting volunteerism and assuming control of cultural institutions like the state history museum in Sacramento.
She also presided over the state's annual California Governor's Conference on Women and Families, turning the event into an affair that drew tens of thousands of women, a raft of celebrity attendees and a crowd of corporate sponsors.
Perhaps her most crucial role as political helpmate came in the waning days of the recall election, after The Times report on Schwarzenegger's behavior. At a rally in San Diego, the actor acknowledged before several hundred chanting supporters that, "Yes, I have behaved badly sometimes."
"Yes, it is true that I was on rowdy movie sets," he went on, "and I have done things that were not right, which I thought then was playful. But I now recognize that I have offended people. And to those people that I have offended, I want to say to them, I am deeply sorry about that, and I apologize."
Appearing alongside her husband later that day at a news conference, Shriver blunted the political impact of the story by vouching for Schwarzenegger, saying the sexual misconduct allegations "show why really good people don't want to go into politics anymore."
"I don't get into specifics," she told reporters. "As I say to my children, it always takes great courage to do -- stand before anybody and apologize," she said. "I think that's what Arnold did today. I think he handled it and his statement speaks for itself."
The two celebrated their 25th wedding anniversary on April 26, a day they let pass without public comment, in contrast to their usual stream of commentary in various social media.
Their postings over the last few months offered a picture of a couple leading separate lives. Since Schwarzenegger left office, he has been jetting around the world, heading to Brazil's Xingu River with director James Cameron, to London for Mikhail Gorbachev's 80th birthday party, to Val d'Isère in France for skiing and to Washington, D.C., to attend a White House summit on immigration.
In late March, Schwarzenegger announced a collaboration with famed comic book creator Stan Lee, saying, "I have never had a conversation with Maria about any of this. I think it will be a big surprise." Shriver mentioned the East Coast college tour and, in early April, visited the Bahamas while Schwarzenegger headed to Cannes to receive the Legion D'Honneur medal.
Photos: A political marriage with star power
Times staff writers Seema Mehta and Maeve Reston contributed to this report.