Eusebio Pedroza was in the Panamanian Senate at the end of his career: http://sportsillustrated.cnn.com/vault/article/magazine/MAG1119481/index.htm
Vitali Klitschko, I guess has to be thought of as a politician, having run for office, and since then has been fighting for the WBC title. But, as far as guys who were actually in office while fighting for a title...I'm not sure. I wonder if Pac's people all support the continuation of his boxing career while being in office.