MP Cat Smith has been named as part of the new shadow cabinet, following a reshuffle amid a revolt against Labour leader Jeremy Corbyn.
Mr Corbyn began a reorganisation of his shadow cabinet, following the resignation of 11 shadow ministers in a day, and more on Monday morning.
Ms Smith, who represents Lancaster and Fleetwood in Parliament, has been given the responsibility of shadow minister for voter engagement and youth affairs.
She was asked to take on the new role on Sunday night, and said she “didn’t hesitate” to accept the offer.
Ms Smith said: “I’ve always had a real interest in engaging with young people.
“Some of the best parts of the job as an MP are going to schools and colleges and youth groups and speaking to young people about politics.
“We have a crisis in voter engagement with young people. I think that’s partly because they don’t feel like they’ve got a stake in it and that’s what I’m hoping to change.
“I’ve already been doing quite a lot of work engaging with young voters, but now I’ve got more of a platform to do that from.”
Ms Smith was promoted to the position amid a revolt from shadow ministers, following the sacking of Hilary Benn as shadow foreign secretary in the early hours of Sunday.
The sacking was followed by a raft of resignations, but Ms Smith said now was “not the right time” for in-fighting.
She said: “I don’t think this is the right time for Labour colleagues to be trying to orchestrate a leadership crisis - why now?
“The country has to come first and, given what happened on Thursday and what we saw on Friday morning, with the pound crashing to a 31-year low, we need to look at the stock exchange - that’s people’s pensions.
“It has an implication for their mortgages.
“For the Labour Party to be looking internally, it is totally the wrong time to be doing that.
“Less than a year ago, Labour Party members voted overwhelmingly, over 60 per cent, to support Jeremy Corbyn rather than the other three candidates - that’s a huge mandate.
“There was such huge support for him and, speaking to my members over the weekend, it was clear the vast majority of my membership was still supporting Jeremy, so I think it’s right that I do.
“If we have a massive internal conversation about leadership, then we’re not offering leadership to the country.”
Despite campaigning to remain in the EU, Ms Smith said she does not believe the referendum should be re-run.