A Wembley Central councillor became the third Labour representative in recent weeks to stand down.
Luke Patterson resigned on December 4, to focus on his family and education career.
He follows Michael Pavey and Sarah Marquis who have both stood down from representing Barnhill ward.
Cllr Patterson told the Times: "I have recently been given increased responsibility in my career in education and due to the birth of my third child, time has become a major factor in my decision. Out of duty to the people of Wembley Central I feel it is only fair on them if I stand down."
Cllr Patterson, who was elected in May 2018, added: "It's important that in this decision I just want to say thank you to all my fellow councillors in all the support they have provided me in the short time I have been elected into post. Thank you to the cabinet members and thank you to all of the officers who I have found to be extremely helpful during my time."
A by-election will be held on January 23.
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