City of Edinburgh Council leader Andrew Burns has announced he will stand down at the 2017 local election.
The Labour councillor said he wants to focus on "personal interests".
The union Unison said Mr Burns has been instrumental in protecting council services from privatisation.
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Mr Burns said: "It's been the political, and professional, privilege of my life to represent those local Edinburgh residents for nearly two decades now.
"Nothing I've done in my life beforehand, and I'm sure nothing that I'll do with my life in the future, will match the hugely enriching local experiences I've had over those two decades.
"But today, I'm confirming that I won't be putting my name forward for a fifth consecutive occasion, and thus will not be standing for potential re-election in 2017."
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He added: "I want to now move on, to focus on a different phase in my life.
"A phase that once again will not involve front-line politics, in any shape or form, whatsoever... I simply now want to focus on some of those personal interests in the next few years of my life. Nothing more, nothing less."
Unison Edinburgh lead negotiator Tom Connolly said: "Andrew has always made himself available to Unison and the other trade unions and has engaged with us on a regular basis throughout his time as leader. He has always done this in a respectful, positive and constructive manner."
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John Stevenson, Unison Edinburgh branch president, added: "Huge challenges face Andrew for the rest of his term of office as local government carries the lion's share of Westminster and Holyrood cuts. Not least of those will be how to stand by the pledge of no compulsory redundancies."
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