Coates entered public office as an alderman on the Lithgow City Council in 1945, where he served for almost forty years.
In 1965, Coates ran as an independent again and won the election on Democratic Labor Party preferences.
[4] With no party winning an outright majority, Coates threw his support to the Liberal-National Coalition–a critical step in allowing the conservatives to form a minority government, ending 24 years in opposition.
Coates held the seat, renamed Blue Mountains in 1966 where he was defeated by Labor's Mick Clough not 1978 references election results for 1976, until he was swept out in the 1978 "Wranslide" by Labor's Mick Clough, his opponent in 1976.
He was a builder by trade, and he went on to succeed his father in running the family business, G.Coates and Sons Pty Ltd, a hardware store and timber yard in Lithgow.