The Labour group has taken control of Wolverhampton City Council with 31 seats.
The group had formerly held 30 seats, the same as the Conservatives and the Lib Dems together. Lib Dem mayor Malcolm Gwinett held the casting vote.
The Labour Group held a vote of no confidence against the ruling group in a meeting held on Tuesday evening.
Lib Dem councillor Claire Darke removed her support for the ruling group and voted with Labour.
Ms Darke is the councillor for Park Ward.