Mr Coles was first elected as mayor in 2004, but said after a 21-year career in local body politics, it was now time to ''take stock'' and move on to something new.
The 69-year-old retired farmer said he had enjoyed ''pleading the case'' for Waimate and its people.
''Over the whole 21 years it has been been quite a piece of my life, that's for sure. And in the last three terms as mayor, it has been very, very rewarding at times but at other times it can be quite a challenge.
''Sometimes you just need to take stock and take a bit of time for yourself.''
He said one particular issue that stood out during his time as mayor was the widening of the Pareora bridge.
''It would have been only a matter of time before there would have been a fatality there ... we managed to get that sorted before that happened, in my eyes.''
Nominations to replace Mr Coles as mayor will not open until July.
The Local Electoral Amendment Bill (No 2), which includes provisions that affect when nominations for this year's local body elections open and close, is before Parliament at present.
If it is passed, nominations for local body amd mayoralty elections will open on Friday, July 19. If the legislation is not approved, nominations will open on Friday, July 26.
