John Haggerty Jr. was sentenced in December 2011 to up to four years in prison. He remained free while he appealed his conviction, which was rejected in February. He surrendered at state Supreme Court in Manhattan on Wednesday.
A jury found Haggerty guilty of conning Bloomberg into putting up $1.2 million for an elaborate 2009 poll-monitoring effort. Bloomberg was then running for a third term.
Haggerty pocketed $750,000 of the money. His lawyer said Wednesday he has repaid it as part of his sentence.
Bloomberg testified for the prosecution during the trial.