Maddison started his first-grade football career with St. George in 1965 and the following year appeared in his first grand final, the last of the Dragons' record-breaking 11 consecutive premiership wins.
He won that first premiership as a centre but later moved into the forwards and enjoyed success in his career as a wide running second-rower.
In the late 1960s after St George had lost the stars of their long reign, Ken Maddison's work ethic (along with the stellar brilliance of Billy Smith and Graeme Langlands) was a factor in keeping the club competitive, regularly finishing in the top five.
1973 was Maddison's career high-point when he became the first forward to win the Rothmans Medal for best and fairest player in the League, edging out Ron Coote by just one point.
Although Maddison played at a time when the loose forwards of the Souths' pack – Coote, Bob McCarthy, Gary Stevens and Paul Sait – dominated representative selections, he managed his Australian debut at the end of a great club season in 1973 when he was selected for the 1973 Kangaroo tour of Great Britain and France.