Recruited from Maryborough, Lock began playing for Melbourne in 1936 as a half forward flanker and was known as the "Bunton" of Melbourne in his early years. In 1939, Lock missed out in playing in the Demons' premiership, due to being suspended. In 1940, Lock again missed being a part of Melbourne's premiership team, after being injured in the preliminary final. He was, however, one of Melbourne's best players, his performance described as "outstanding", in their 1941 premiership side.
In 1942 Lock enlisted in the Australian Army to serve in World War II. He held the rank of corporal and served in the 4th Field Ambulance. He was discharged on 4 January 1946 after the conclusion of WWII.
After being discharged from the Army, Lock began playing for Melbourne again in 1946. He was Melbourne's best and fairest in 1947. He was also named in the Sporting Life "Team of the Year" in 1947. In 1948 Lock injured his knee in a semi final and again missed out on playing in a Melbourne premiership. After playing only four games in 1949 due to the knee injury suffered in 1948, Lock retired in the 1950 pre-season when he found out the knee was "not likely to respond to treatment".
Lock was made a life member of the Melbourne Football Club in 1946. Lock was a boyhood hero of Ron Barassi. Barassi described Lock as someone who "combined strength with guile and football intelligence" and "was dashing and played with flair". He was named on the interchange bench in Melbourne's official 'Team of the Century'.