Mellus attended Villanova University from 1934 to 1937, where he played football. In 1937 he was named to the New York Sun's collegiate All-America team (first-team) and to the Associated Press's 13th annual collegiate All-America team (second-team).[2][3]
Mellus was drafted in the ninth round of the 1938 NFL Draft.[4] In 1938, Mellus played for the New York Giants on their championship team, and on their teams of 1939 to 1941. In December 1941, he was named to the first-team of the Associated Press's NFL All-Star team.[5] After being drafted into military service in February 1942, Mellus played for the Eastern Army All-Star Team. In December 1943, he was named to the Associated Press's military service All American team.[6]
Following his discharge from the military, Mellus played in 1946 for the San Francisco 49ers and from 1947 to 1949 for the Baltimore Colts. He was inducted into the Luzerne County Sports Hall of Fame in 1988,[7] and into the Villanova University "Wall of Fame" in 2002.