Brent Council's leading Labour group has lost a second councillor in the space of two months.
Cllr Abdizarak Abdi resigned on April 29 following the annual council meeting.
He continues to serve Kilburn as an Independent and so there will not be a by-election.
Kieron Gill stepped down as a councillor in March, having represented the Brondesbury Park ward.
In February Mr Gill was the only Labour councillor to abstain on the council's budget. He later declined to comment on the circumstances leading to his resignation.
A by-election for the Brondesbury Park ward is taking place on Thursday (May 6).
Both men were newly elected during the 2018 elections when Labour swept to victory, ousting three Conservatives who had held Brondesbury Park for more than a decade.
Cllr Abdi declined to comment on his resignation from the Labour group when contacted by this paper.
In 2018 Cllr Abdi was removed from the planning committee. He claimed it was because he voted the wrong way on applications and made formal complaints against leader Cllr Muhammed Butt, alleging a “breach of members’ code of conduct” and "political interference" in the planning system. The complaints were later thrown out.
Brent leader Cllr Muhammed Butt said: “Cllr Abdirazak announced his decision following last Thursday’s annual council meeting.
"I asked him if he was certain that this was what he wanted to do, he said that he needed to make a change but did not elaborate.
"With regard to Kieron Gill, his was an actual resignation as a councillor for personal reasons, hence tomorrow’s by-election.”
He added: “Being a local representative is a big commitment – if a sitting councillor feels that they can no longer do what they committed to doing, regardless of how long they’d been in office, then standing down and giving local people the chance to elect a new representative is entirely the right thing to do."
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