Cllr Jim Grant has stood down as leader of Swindon Borough Council's Labour Group after more than a decade in the key role.
His newly-elected replacement is Cllr Jim Robbins.
Cllr Grant, who represents Rodbourne Cheney, said: "I’m immensely proud of each of my Labour councillors as well as all of the hard working members across North Swindon and South Swindon constituency parties for their hard work and dedication that contributed to the gains we made last Thursday.
"It was easily the most successful election we’ve had in years and now gives us a platform from which we can seek to take control of the council next year. I think we are all heartened by what happened and it has given both the Group and the wider party renewed enthusiasm which will help achieve our goal.
“Reflecting on the situation over the weekend I have come to the conclusion that now would be a good time for me to stand down as Leader. I have been in post for over 10 years and think that is too long for anyone and I believe a new leader needs time to bed themselves into the role and to build on, and develop a relationship of trust with the people of Swindon.
“I do not intend to step away from politics in any way shape or form. I shall be seeking re-selection for Rodbourne Cheney this year and want to focus my time on campaigning activities helping and supporting the campaign locally.
"It has been a privilege to lead such a committed and inspiring group of councillors. I am sure you (or we, as I should say now) will give my successor that same source of commitment and inspiration."
New leader Cllr Robbins, who represents Mannington and Western, said: "I am honoured and proud that my Labour colleagues have elected me as Leader of the Labour Group. Last Thursday was a turning point for Labour in Swindon. Voters are fed up with the Conservative council here in Swindon, and a Conservative government in Westminster.
“I’m raising my family in Swindon and I want Swindon to be a place of opportunity; life chances for all and be a place where people want to spend time with their families. I’m relishing the opportunity to lead the Labour Group and build on our recent successes."