Rebel councillor Steve Collier has resigned from the Labour Party after being an active member for 20 years.
The South Portslade member of Brighton and Hove City Council has clashed with colleagues on a number of issues and on some of them did not support the official line in crucial votes.
He said: "In principle and practice I could not endorse or support the out-of-touch line the council's administration was taking."
Coun Collier was against having a directly-elected mayor and also opposed a park-and-ride scheme north of the Brighton bypass.
He said: "I have always been honest and dedicated to what I feel and believe. I will continue to challenge those issues affecting people and the environment."
Coun Collier said the people of South Portslade, where he has been a councillor since 1991, would remain close to his heart.
He added: "I sincerely hope there is some sort of radical change of direction in the Labour Party, especially on the council but this will have to be without my contribution, whether by word, thought or deed."
Coun Collier will continue to sit as an independent Labour councillor until the local elections in May next year.
Then the number of councillors in South Portslade reduces from three to two. At a selection meeting earlier this year, he was not chosen by Labour to contest the seat.
Deputy council leader Jackie Lythell said: "I am always sad when someone feels he has to leave the Labour Party.
"It is not exactly unexpected as he has been unhappy for some time with some of the decisions that we have had to make."
Labour remains in charge of the 78-member council which also has Conservatives, Liberal Democrats, Greens and an independent.
Comments: Our rules
We want our comments to be a lively and valuable part of our community - a place where readers can debate and engage with the most important local issues. The ability to comment on our stories is a privilege, not a right, however, and that privilege may be withdrawn if it is abused or misused.
Please report any comments that break our rules.
Read the rules hereComments are closed on this article