Close spiritual and political associates urged him to instead fight to restore his constituents' - and his family's - trust and finish out the 18 months left in his last term.
"Resigning would be the easiest thing to do," he said he thought.
He's sticking it out and faces endless questions about the affair, whether he used public money to visit his lover and whether his 20-year marriage will continue. Add to it a barrage of criticism from South Carolina politicians who think the two-term Republican should step down.
"Part of walking humbly is you've got to listen to your critics out there," the 49-year-old Sanford said. "And all of us will have critics, and the higher you go, I suppose, the more critics you have."
Sanford spoke exclusively with The Associated Press outside his family's beach house on Sullivans Island. He, his wife, Jenny, and sons were in separate cars, headed to his family's farm - where his 83-year-old mother lives - in Beaufort, an hour south.
The governor admitted last week to a yearlong affair with the woman from Argentina who he says he's known for about eight years. Later Sunday, 41-year-old former television reporter Maria Belen Chapur acknowledged in a statement that she had been having a relationship with the governor.
Sanford looked like a man of leisure in faded khaki shorts, T-shirt and bare feet. But behind the casual attire, he appeared contrite and spoke of falling from grace and rebuilding his life.
"I am sorry," he said. "I apologize for letting everyone down."
The Sanfords say they will try to reconcile. One person they've sought help from is their spiritual counselor, Warren "Cubby" Culbertson, whom Mark Sanford thanked during the news conference in which he admitted his affair.
Reconciling with fellow lawmakers and constituents also lies ahead. Some lawmakers want his resignation because he secretly visited his mistress during a state-funded 2008 trip, and because he was out of touch with his staff during his recent weeklong visit to Argentina to see her. His staff had told the public he was hiking the Appalachian Trail before the real story of his mysterious absence came to light.
Sanford has agreed to reimburse the state for some of the more than $8,000 in taxpayer money spent on the Argentina leg of the economic development trip to South America last year. On Sunday, he repeatedly said he never used public money to see the woman.
Chapur, a divorced mother of two sons, said in a statement to news network C5n of Buenos Aires that said she will not talk about her private life, which has already been the focus of intense media scrutiny in the U.S. and Argentina.
Chapur, a graduate in political science from the Catholic University of Buenos Aires, said someone accessed her Hotmail account without permission late last year and leaked e-mail correspondence that described a relationship with Sanford to the South Carolina newspaper The State.
"I have decided to send this statement to clear up certain incorrect things that are being reported, and put an end to a matter that, as you imagine, is very painful to me, my two children, my entire family and close friends," she said in the statement addressed to anchor Eduardo Feinman, who read it on camera. Feinman was Chapur's editor when she worked briefly as a television reporter in 2001.
When it comes to his critics - most notably Republican state Sen. Jake Knotts - and their calls for him to step down, Sanford said he understands where they are coming from.
"I don't begrudge the Jakie Knottses of the world," Sanford said. "He's going to do what he's going to do. I gotta do my part."
The governor's efforts to stay in office appear, in the minds of some lawmakers, to hinge in part on his ability to salvage his marriage. While several critics wants a criminal probe and others want him to step down, reconciling with the first lady does have sway among legislators.
"That's almost become a proxy for how some are looking at this. They're looking at Jenny," said state Sen. Tom Davis, a Beaufort Republican and former Sanford chief of staff. "In large measure, it depends on how things work and how people see things are working out between the governor and first lady."
As far as his marriage, Sanford said he and his wife are working on it.
"If there wasn't healing going on, I wouldn't be here," he said, pointing to his beach house, where he had dinner with his family Saturday night and where he took a run at sunrise on the sand with one of his sons.
Sanford added that he has been overwhelmed by the support he's received.
"It's only in the hard times you get a sense of how blessed you really are," he said.
Regardless of what politicians in the Statehouse think, his Sullivans Island neighbors are supportive.
During Sunday's interview, several folks stopped to say hello as they strolled by on their morning walks. One man, driving a golf cart festooned with red-white-and-blue decorations, paused to invite Sanford and his family to a Fourth of July celebration.
"How are you?" the man asked Sanford.
"Considering the circumstances, all right," Sanford replied with a wan smile.