Recruited from the Melbourne Teachers Training College, he played his first senior VFL match for Carlton on 18 May 1912, on the half-forward flank, against Collingwood, at Princes Park.

He transferred to Melbourne, playing his first senior match on 6 June 1914 against University (he scored three goals).

He was suspended for three weeks, when playing for Carlton, in June 1913 for elbowing Allan Belcher in a spiteful match against Essendon on 21 June 1913 (Belcher was suspended for four weeks for elbowing Williamson).

[4] In May 1919, an unidentified former Melbourne footballer, wrote to the football correspondent of The Argus as follows: He enlisted on 19 June 1915; and, according to his service record, he held the rank of sergeant whilst training, was promoted to second lieutenant on 1 February 1916, to lieutenant on 10 March 1916, and to captain on 4 July 1916.

Williamson received the Commander in Chief's Congratulatory Card for showing "bravery and initiative".