Gia Arnold, 24, is a married mother of three who was running for the Republican nomination for state Senate in a western New York district.
Early Thursday, the tea party favorite sent an email to the media confessing the affair, which she said had begun just this month with a friend.
"I have made personal decisions that have ultimately resulted in the necessity of my stepping down from the campaign," Arnold wrote.
"I participated in an extramarital affair beginning in August of this year. It was an excuse for an escape from an already declining marriage. I cannot regret the decisions I have made, but I can admit to being happier presently than before."
"It is for my ex-husband, my children, my family and friends that I must publicly admit to my actions, as I believe honesty and integrity are of utmost importance in life."
Arnold told the New York Post that the affair began on August 1 and she decided to drop out of the race to take control of the situation, blaming it on "an unhappy marriage [that] led to poor decisions."
The primary, in which Arnold was competing against North Towanda Mayor Robert Ortt, is set for September 9. Arnold will still appear on the ballot, but she will stop actively campaigning.
The 62nd state Senate District is currently represented by Republican George Maziarz, who announced last month he would not seek another term after 19 years in office. Maziarz said he had planned to retire for some time -- and endorsed Ortt -- but is also under federal investigation for his campaign expenditures.