[1] A Republican, Mruk ran unsuccessfully for member of the Erie County Board of Supervisors in 1933, and a seat on the Buffalo Common Council in 1935.

[1] As a result, he became unpopular with the Republican leadership, who endorsed his 1944 primary opponent, Edward J. Elsaesser[1] After leaving Congress, Mruk returned to active management of his jewelry store.

[1] Mruk won the 1949 mayoral election against the Democratic nominee, Chief City Judge Joseph Hillery and two other candidates.

[1][2] His campaign was buoyed by Polish-Americans who usually voted for Democrats, but were unhappy that the Soviet Union had in fact made Poland part of the Eastern Bloc following World War II.

[1] Mruk served from January 1, 1950, to December 31, 1953, and his time in office was highlighted by his concentration on rebuilding the city's infrastructure, including streets, bridges and viaducts.

[1] Relying on his business experience to master the details of Buffalo's budgets and spending, Mruk took pride in effecting most of his programs without having to increase local taxes.