Jon Cruddas has backed a Barking and Dagenham councillor to fill his seat when he steps down as an MP.
Mr Cruddas, who has been an MP since 2001, announced in August that he would not be standing for re-election.
Cllr Margaret Mullane has launched her campaign to be Labour's candidate to replace him as Dagenham and Rainham MP.
Ms Mullane, who manages Mr Cruddas's office, has been a Barking and Dagenham councillor since 2010.
She served on the cabinet as lead member for community safety and enforcement from 2018 until earlier this year.
Mr Cruddas said she has his "full support", adding: "There is no-one better placed to take on the challenge of representing the people of Dagenham and Rainham in Parliament.
"Margaret was born and raised in the constituency and has been at the heart of my office, managing it, for 13 years.
"She knows the struggles local people face and is the only person I have faith in to win the next election.
"Margaret will be an exceptional MP."
Ms Mullane began her campaign with a social media video, in which she said her family was raised in council houses in Baddow Close and Groveway in Dagenham.
She went to St Peter's School in Dagenham and the trade union member explained that "working-class values are in my blood".
Ms Mullane said: "I will put community at the heart of my campaign.
"I am thrilled to have the support of Jon Cruddas MP. If I could continue in his work, it would mean so much.
"Dagenham and Rainham is in my heart and I'm fiercely proud of our constituency."
The last general election was in December 2019 and one must be held at least every five years.
Mr Cruddas was elected to represent Dagenham in 2001 but Rainham was absorbed into the constituency after a boundary change in 2010.
In an interview with this paper in August, he felt it was the right time to move on with the Tories in “crisis” and Labour “in a strong place”.
On his decision, Mr Cruddas added: “It was really mixed emotions to be honest, because I’ve absolutely loved the job,"
"It’s been an incredible privilege - I never thought I’d be an MP."
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