An announcement would come soon, the aide told CNN Thursday.
"He's looking all but certain to do it," the former top aide to Sanford said, speaking anonymously.
The former aide said Sanford would seek the Republican nomination for the state's 1st Congressional District seat being vacated by Scott, who was appointed to the U.S. Senate earlier this week by Gov. Nikki Haley.
The Republican primary likely will happen in late March per the state law's requirement that the primary must take occur 11 weeks after Scott officially resigns his House seat.
He is expected to resign in early January, CNN said. Scott is filling the Senate seat vacated by Jim DeMint, who resigned to lead the conservative Heritage Foundation.
If no candidate earns a majority of votes, a runoff election would take place two weeks after the primary. A special election would be in May.
Sanford, who lives in Charleston, represented the 1st Congressional District from 1995 to 2001. After three terms, Sanford ran successfully for governor twice and considered a 2012 presidential bid before an extramarital affair upended his national ambitions.