Jacqui Williams has represented the Stanley and Outwood East ward on Wakefield Council since 2004.
Coun Williams, 78, is one of six Labour members who will not contest their seats again at May's local elections.
Her party colleagues Harry Ellis (Knottingley), Elaine Blezard (Normanton) and Sandra Pickin (Hemsworth) are also standing down.
Wakefield North councillor and current mayor Tracey Austin confirmed her departure in January, while Wakefield East's Olivia Rowley was deselected in her ward as the party candidate for this year's polls.
Councillor Williams, 78, said: "It's been a pleasure and a privilege working with residents and for them.
"I've done it for 18 years and if I hadn't thoroughly enjoyed it then I don't suppose I'd have done it for that long!"
She joked: "I did try to go four years ago and the Labour group wouldn't let me, so this time my mind was made up!"
Coun Williams said that working with local groups and charities during the pandemic had been a "stand-out" moment, as it demonstrated "community spirit is still very much alive" in the area.
She added: "Being mayor for the year was a highlight. We did over 500 different things and raised £21,000 for local charities. It was a brilliant experience, and again, a privilege."
Besides enjoying retirement, Coun Williams said she would still be involved in community activities, including at the Outwood-based day centre Move Ahead, which helps people affected by brain injuries.
Meanwhile, Councillor Ellis said he was standing down from his Knottingley ward for personal reasons.
He said he would "definitely miss" being an elected member, having been one since 2010.
He added: "I was hugely proud to represent them as mayor in 2016/17.
"There’s only been two mayors from Knottingley and I've been one of them.
"Just helping people, that’s all I wanted to do as a councillor. Being a spokesman for people. I didn't want any personal gain from it."
Councillors Blezard and Pickin are also standing down from their seats following a combined 28 years of service.
Coun Blezard has represented Normanton since 2006, while Coun Pickin, who is also the chair of the council's planning committee, has served Hemsworth since 2010.
In a separate development, fellow Labour councillor Dick Taylor was deselected by the party in Featherstone as their election candidate, but he announced on Wednesday that he will stand again as an independent.
Local Democracy Reporting Service