Jon Lansman, the founder of Momentum, has withdrawn his candidacy to become Labour Party general secretary.
It had been reported widely last week that Jeremy Corbyn, the Labour leader, had called Mr Lansman in an attempt to dissuade him from standing in the election to succeed Iain McNicol, who is stepping down from the role.
Mr Lansman, who was elected to Labour’s national executive committee earlier this year, announced his decision not to contest the post on Twitter on Sunday.
He said his aim in standing had been to “open up the contest” and instigate a debate on the development of the party.
“With my aims fulfilled, I have decided to step back from the race to focus on my role on the NEC,” he explained.
Mr Lansman, whose group was instrumental in propelling Mr Corbyn to the party leadership, said a number of party members had informed him they were planning to stand for the post.
Ordinary party members must be encouraged to step forward and take responsibility, he said.
Focusing on the NEC, he said he would “work with members and affiliates to replace the old top-down model with modern, open, and transparent, pluralist, participative democracy”.
The Labour leadership is believed to support Jennie Formby, the former political director of the Unite trade union, as the candidate to succeed Mr McNicol and had feared a split in the left vote if Mr Lansman had stood.