CHARLESTON, South Carolina (Reuters) - Former South Carolina Governor Mark Sanford, whose political star faded nearly three years ago after revelations of an extramarital affair, plans to return to politics and run for a seat in the U.S. House of Representatives, he said on Tuesday.

Sanford told Reuters he intends to make a formal announcement on Wednesday.

The 52-year-old Republican will seek an open House seat left vacant by the recent appointment of first-term Republican Representative Tim Scott to the U.S. Senate.

A special election for the seat in South Carolina's First District will be held this spring.

Scott replaced former Republican Senator Jim DeMint who resigned in December to head the conservative Heritage Foundation.

Sanford, a two-term governor and former congressman, was seen as an early contender for the 2012 Republican presidential nomination. But in 2009, he disappeared from his office for a week on a trip to visit his Argentine mistress. Aides said he was hiking the Appalachian Trail.

When he returned to South Carolina, Sanford gave a tearful press conference admitting he had been unfaithful to his wife and called the Argentine woman, Maria Belen Chapur, his "soul mate."

The affair ended Sanford's presidential hopes and his wife divorced him. He was censured by the South Carolina legislature for leaving the state secretly but served out the rest of his term, which ended in 2011.

Sanford and Chapur were engaged last year. Continued...