Mrazek served in the United States House of Representatives from 1983 until he retired in 1993. Freshman members usually do not sit on the House Appropriations Committee, but Mrazek persuaded Speaker of the House of Representatives Tip O'Neill to make an exception for him. After being elected to his fifth term in Congress, Mrazek announced that he would not stand for re-election, choosing instead to explore a run for the United States Senate in 1992. He abandoned this race after being swept up along with hundreds of other members of Congress implicated in the House banking scandal.