Sanford, a one-time rising Republican star mentioned as a possible presidential candidate, said in a statement to CNN that he and Maria Belen Chapur are "both happy and excited" about their engagement.
"I have long expressed my feelings for her, she's a wonderful person," Sanford said. "My closest friends have met and love her, and I look forward to introducing her to still many more that have yet to do so."
Sanford's political career quickly unraveled in 2009 when he disappeared for five days on what he said was a hike on the Appalachian Trail. Sanford later admitted during a rambling and sometimes tearful news conference that he was in Buenos Aires with Chapur, whom he called his "soul mate."
Sanford and his wife, Jenny, divorced in 2010. Jenny Sanford had said she discovered the affair in 2008 when she found a copy of a letter her husband had written to Chapur.