In a lengthy resignation statement, Mahmood said: “I joined and supported Labour for the best part of my life because I believed in a political movement rooted in working people, strong local democracy, equality, genuine internal pluralism.
“I no longer believe it reflects those principles.”
The councillor also criticised Birmingham Labour’s leadership, claiming there was a “consistent culture of avoidance and opacity” and that questions from members were often ignored.
He added: “In my view, the current local leadership lacks the experience, judgement, and political competence required to effectively manage a group in a city as complex and demanding as Birmingham.”
Among other reasons for leaving, Mahmood raised concerns about Labour’s immigration policy and the party’s handling of the conflict in Gaza.
He also said expectations were placed on councillors to support the appointment of Reform UK members into influential committee positions.