Mills usually played as a ruckman but was also used at centre half-back. He captained Hawthorn at various times during his career, starting in 1932, then the 1934 and 1938 seasons before his final stint from 1940 until 1941 which was as both captain and coach. During his time at Hawthorn he won their Best and Fairest award three times, in 1933, 1935 and 1939. He also represented Victoria in interstate football, doing so on 11 occasions.
He was named on the back pocket in Hawthorn's official 'Team of the Century'.