He served as the head coach for the Pittsburgh Steelers of the National Football League (NFL) from 1948 to 1951, compiling a record of 20–26–2.

Michelosen got his start in football playing quarterback at Ambridge High School, under coach Maurice "Moe" Rubenstein.

Michelosen held on to the distinction of being the youngest coach ever to start an NFL season until the Oakland Raiders hired Lane Kiffin in 2007.

Michelosen was an influence on NFL greats such as Mike Ditka and Marty Schottenheimer, both of whom were born and raised near Pittsburgh and played for Pitt in the 1950s.

Michelosen also has a place in the civil rights history of the country, guiding the first team to break the color barrier in the southern bowls.

In the 1956 Sugar Bowl, Pittsburgh became the first sports team ever to field an African American player in the deep south.