The longest-serving member of is stepping down as leader of the city's Liberal Democrats group to "pass on the baton to someone younger".
Veteran councillor Paul Tilsley, aged 70, has led the city's Lib Dems since June 2005 and will leave the post later this month.
He immediately became deputy leader of the council as junior partner in the Tory-Lib Dem coalition which ran the city until 2012.
READ MORE: {}
During that time, he oversaw the controversial business transformation project which modernised the council's offices and IT systems.
While it is credited with having saved the authority £1 billion over ten years, it has also been blamed for landing the which has been deemed too expensive during the austerity era.
As one of the highest-ranking Lib Dems in local government, Coun Tilsley also enjoyed a close relationship with former Deputy Prime Minister Nick Clegg - particularly as at the time both were working as junior partners in coalition with the Conservatives.
But the coalition relationship did not stop him criticising the last Government for the "draconian" cuts forced on councils.
His resignation means the group's 11 councillors will meet at the end of January to elect his successor with deputy leader Jon Hunt likely to be a front-runner to succeed him.
Most Read
Coun Tilsley has been a member of the council for 42 years in total, having been first elected in 1968.
During that time, he has been awarded a CBE and served as Lord Mayor of Birmingham.
The veteran politician says he will continue as Sheldon councillor at least until his term of office ends in 2018.
He said: "It is now time to stand aside and hand the baton to someone younger.
"It has been an honour and privilege to lead the group and play a central role in the leadership of the largest local authority in Europe.
"Under the previous system of measurement, as the cabinet member responsible for improvement, we went from an under-performing council with one star to three stars, recognised as 'Good' nationally, something that I am very proud of."
Lib Dem deputy leader Jon Hunt (Perry Barr) paid tribute: "Paul is a veteran of Birmingham politics with decades of experience as a city councillor and a long-standing reputation as a big hitter.
Don’t miss
"In his youth in the 1960s, he was a pioneer of what we know as community politics - an approach to looking after residents and working with communities that has been a major inspiration for people such as myself and for the Liberal Democrats as a whole.
"We all look forward to him finding new roles and we in the Liberal Democrats need to ensure we continue to benefit from his experience and knowledge.
"He was deputy leader of the council during the years of the Progressive Partnership, which is fondly remembered by many residents, particularly in the light of the chaos of the last three years under Labour.
"Leading us in opposition, he has kept us together in a time of severe pressure and led a group that has proved itself effective in opposition - in spite of setbacks."