Coun Peter Williamson, who represents Upper Lune Valley Ward, will not be standing as a Conservative councillor in the local elections in May.
Coun Williamson was elected in 2007, and became leader in 2011.
He said: “After they de-selected me, they were happy to let me continue as leader until the elections in May. But I won’t be standing again.”
Coun Nigel Goodrich, who represents Silverdale Ward, has also been de-selected from the Lancaster City Council Conservative group.
Former Lancaster City Council Conservative group leader Coun Roger Mace, who represents Kellet Ward, was also told he could not stand in the 2019 elections.
He said in October 2018 that “the individuals responsible for my treatment have no right to look to me for support in the future”.
Coun Brett Cooper, who represents Bare Ward, resigned from the Conservative Group last year, and now stands as a non-aligned independent.
Last year, Coun Cooper described his fellow Tory colleagues as “sad and pathetic”.
Coun Charlie Edwards, who also represents Bare Ward, had the whip removed by the Conservative group last week in a row over council tax, meaning he currently sits as an independent.
However he has said he will be standing as a Conservative for Bare in the elections in May.
The Labour leader of Lancaster City Council, Coun Eileen Blamire, announced her retirement last year.
Completed nomination forms for the elections on May 3 will be accepted at Lancaster Town Hall from Monday March 18 between 10am and 4pm.
The deadline for receipt of nominations is 4pm on Wednesday April 3 and the full list of candidates will be released once nominations have closed.