Waldemar Mrusek was born in Gleiwitz, Germany on May 11, 1926. He first made his name as a goalkeeper in local soccer in Gleiwitz.
In the summer of 1949 Waldemar joined VfL Osnabrück from BV Cloppenburg. He played in 30 league games for Osnabrück in the Oberliga Nord in the 1949-50 season. The club finished in third place behind winners Hamburger SV and runners-up St. Pauli. In fourth place were Werder Bremen.
In the 1950-51 season he played for 1. FC Köln but failed to make any league appearances in the Oberliga West. From 1951 to 1954 he played for Fortuna Köln in the 2. Oberliga West.
In 1954 Waldemar became the first professional player that the Toronto Polish White Eagles imported from Europe. He shared the goalkeeping duties with Ted Piskozub in the 1954 National Soccer League season. However, the goalkeeping duo failed to save the White Eagles from a bottom-place finish in the 11-team league. During the season Waldemar was picked to represent the National Soccer League All-Star team.
In the 1955 National Soccer League season he played for Olympia. He then moved to Ulster United.
Waldemar passed away in Toronto in 1979.