Coun Darren Clifford, who represents Harbour Ward in Morecambe, announced his resignation on social media.
He said: “After 40 years delivering leaflets, 33 years as a member, 13 times as a candidate and a combined 16 years as a councillor on three separate authorities, I have today left the Labour Party.
“I will continue to serve my residents, initially at least, as an independent.”
The Lancaster Guardian has contacted Coun Clifford for comment.
He said he would comment on his reasons for resigning from the party in due course, but that he was “greatly reassured by the supportive comments of friends, former colleagues and residents”.
Lancaster City Council now has 20 Labour councillors, 14 Morecambe Bay Independents (MBIs), 12 Conservatives, 10 Greens, three Liberal Democrats, and one independent.