"I am now filing for divorce," she said in a statement. "This came after many unsuccessful efforts at reconciliation, yet I am still dedicated to keeping the process that lies ahead peaceful for our family."
Sanford moved out of the South Carolina governor's mansion with the couple's four children in August.
"I remain thankful to so many across this state and nation for their words of encouragement and prayers during this difficult time," she added. "Please know the boys and I are doing well and are blessed with the incredible support of friends and family and bolstered by our faith and the unfailing love of our God above."
In a statement, Gov. Sanford accepted responsibility for his actions, which he said drove the couple to "this tragic point."
"While it is not the course I would have hoped for, or would choose, I want to take full responsibility for the moral failure that led us to this tragic point," he said. "Jenny is a great person, and has been a remarkable wife, mother and First Lady. She has been more than gracious these last six months and gone above and beyond in her patience and commitment to put the needs of others in front of her own."
The governor echoed his wife's request for privacy at this time.
"We respectively ask for your prayers," he continued.
"It's been a crazy year. ... Certainly his actions hurt me, and they caused consequences for me, but they don't in any way take away my own self-esteem. They reflect poorly on him," she said, in an exclusive interview as part of Walters' "10 Most Fascinating People of 2009."
Sanford was thrust into the national spotlight when her husband confessed that he had been secretly visiting his longtime lover in Argentina instead of hiking the Appalachian Trail, as he told his staff.
Sanford said she found out in January 2009 that her husband had been unfaithful, and she moved out of their house a few weeks before the scandal broke.
"I knew he had been having an affair. I didn't know he was in Argentina," she said.
After discovering his infidelity, Sanford said she told her husband not to visit his mistress and instead consider the consequences for his family.
"What people didn't know was that I had asked Mark to leave. … Without permission to see his woman in Argentina or to see her anywhere, and he was to have no contact with the boys or myself for 30 days. And my hope was that he would wake up from whatever he was in the throes of and maybe see what he might lose."
But he did not wake up. And in the face of every political spouse's nightmare, Sanford broke the mold. She did not stand by her husband's side during his June press conference when he confessed to cheating. Sanford told Walters that the governor didn't ask her to.
"I wouldn't have. If he had asked me, I would have said no," she said.
First Lady on Mark Sanford's Affair: 'We Never Forget'
Though she initially offered support for her husband, Sanford moved out of the governor's mansion in August. Her husband, who is facing impeachment charges, visits their four children who range in age from 11 to 17 on weekends.
She said when her husband called his Argentine mistress his "soul mate," "it hurt."
Sanford, a former investment banker and Georgetown alumna, was 27 when she married the governor 20 years ago. Many called her the woman behind the man, running his campaigns while raising their sons.
Sanford told Walters that she has no political ambitions of her own. "I have no interest. I never have," she said.
While she has forgiven her husband for his transgressions, she told Walters she has not forgotten.
"No, we never forget," she said. "That's a different story."
Sanford's memoir, "Staying True," will be published in April 2010.
A special Barbara Walters hour interview with Sanford will air early next year, in conjunction with the book's release.