St Helens North MP Conor McGinn will serve on Labour’s frontbench, a matter of months after being elected to Parliament.
Mr McGinn has been handed the role of opposition whip by the party’s new leader Jeremy Corbyn and will serve under chief whip Rosie Winterton.
He said: “I’m honoured to be joining Labour’s Frontbench team and look forward to playing my part in helping to hold the Government to account and to get Labour’s message across in Parliament.
“I’m delighted to have been appointed to the Whips Office to work as part of a committed team of colleagues under our Ms Winterton MP.
“I’ll continue to speak out and stand up for my constituents and St Helens North in Westminster, and keep working hard to bring about a Labour Government which people in communities like ours so desperately need.”
Mr McGinn backed neighbouring Leigh MP Andy Burnham in the recent leadership race. Mr Burnham has subsequently been installed as shadow home secretary having finished second behind Mr Corbyn.
The St Helens North MP’s first significant test in his new job may come in the lead-up to the House of Commons vote on airstrikes in Syria to tackle Islamic State.
Senior Labour figures - including several in the new shadow cabinet - are said to be preparing themselves to back the government on intervention despite Mr Corbyn’s preference to oppose.
And so the Labour whips may have their work cutout to convince members to toe the party line.