Judith Church, the MP for Dagenham, announced her decision yesterday, citing "personal family reasons".
Ms Church, a former trade- union official, made her reputation as a keen moderniser when she sat on the party's ruling National Executive Committee from 1992 to 1994.
She was elected in a by-election in 1994 and caused anger among her former employers, the Manufacturing Science Finance trade union, when she gave enthusiastic backing to Tony Blair's New Labour project.
The MP was recently attacked for her poor attendance record in the House of Commons, but her supporters have pointed out that her absence was due to illness.
Ms Church's marriage broke up just before the last general election and friends say that she has found it difficult to cope as a single mother.
"It has been a great privilege to represent the people of Dagenham in Westminster and I have enjoyed this task. My work as an MP will continue until the next election," she said yesterday.Reuse content