She said she asked her husband to leave two weeks ago and to not contact her or their four sons, which explains why the family was unaware of the governor's whereabouts during his unexpected disappearance.
"When I found out about my husband's infidelity I worked immediately to first seek reconciliation through forgiveness, and then to work diligently to repair our marriage," she said in a release. "We reached a point where I felt it was important to look my sons in the eyes and maintain my dignity, self-respect, and my basic sense of right and wrong."
But South Carolina's first lady hinted that she was willing to forgive her husband and that "this trial separation was agreed to with the goal of ultimately strengthening our marriage."
Invoking the Bible, she said: "I remain willing to forgive Mark completely for his indiscretions and to welcome him back, in time, if he continues to work toward reconciliation with a true spirit of humility and repentance."
The couple started their careers on Wall Street, where Jenny Sanford was a vice president in mergers and acquisitions at the investment bank Lazard Freres, the Associated Press reports. The couple met in the Hamptons, Long Island, married and heading to South Carolina
When the governor was asked today whether he was separated from his wife, he responded: "I don't know how you want to define that. I'm here, she's there. I guess in a formal sense we're not."
An emotional Sanford, who spoke about "God's law" several times in his press conference, said he needed a break from his job after what he called an "exhausting" battle against President Obama's stimulus bill.
Sanford did not answer a question from a reporter asking him whether he would resign as governor, but he did say in a written statement afterward that "I'm going to devote my energy to building back the trust the people of this state have placed in me."
"What I did was wrong, period, end of story," Sanford said at the press conference. "I'm committed to trying to get my heart right. ... This was selfishness on my part."
This is the second such scandal to rock the GOP this month. Earlier this month, Sen. John Ensign, R-Nev., admitted to an affair with a campaign staffer and resigned as leader of the Republican Policy Committee.
Almost immediately after Sanford's resignation as chairman of RGA, the organization announced that Mississippi Gov. Haley Barbour will take over as chair.
"My job allows me to share the joys of getting to know great leaders around the country and experiencing great pride when they succeed, but the other side of that is experiencing deep disappointment when they fall short," said RGA executive director Nick Ayers. "Today is undeniably a disappointing day."
South Carolina residents expressed mixed views.
"Here you are cheating. That doesn't stand right with me at all as a woman," Zippora Gregory told ABC News.
"It's happened in politics before and I'm sure it's never going to end," said Camillo Miller.
Sanford returned to work today after nearly a week-long unannounced hiatus.
Earlier this week, his staff told reporters that the governor was hiking on the Appalachian Trail, but this morning the governor told The State newspaper upon his arrival at the Atlanta airport that he was in fact in Buenos Aires, Argentina.