Cllr Roberts decided to step down as Group Leader, a position he has held since May 2016, due to work commitments.
Cllr Mark Hunter became Group Leader and Cllr Lisa Smart became Deputy Leader following Group elections on Monday.
Cllr Iain Roberts said: “It has been a tremendous honour to lead the Lib Dem Group over the past year. We have held the new Labour administration to account and actively campaigned to highlight national issues, protect services our residents rely upon and to fight off the excesses of the proposed GM Spatial Framework.
“I have been ably supported by Mark as my Deputy Leader and I know the Group is in safe hands with him as Group Leader. He will be just as ably supported by Lisa Smart.”
Cllr Mark Hunter said: “We are all very grateful to Iain for the leadership he has shown and his hard work over the past year. That the Group is in such a good shape to continue to challenge the Labour administration is in no small part due to his efforts. It was an honour to serve as Leader between 2002 and 2005 and I relish the opportunity to return to this role.
“Our initial job is to continue to constructively oppose Labour who, in their informal alliance with the local Tories, continue to operate as a minority administration.
“The Liberal Democrats are campaigning for a Stockport Council run in the interests of residents – that is what people will get if they elect Lib Dem councillors in next year’s local elections.”