The Liberal Democrats have confirmed Sarah Olney as their candidate to run against Zac Goldsmith in the Richmond Park by-election.
Ms Olney, who is relatively unknown, currently represents the party in the south-west London seat, and is seen as the main threat to the former Tory MP in the by-election to be held on December 1.
Her selection comes in spite of speculation that the Lib Dems would parachute in a high-profile party figure to shore up their prospects of seizing a constituency they think is winnable.
Leader Tim Farron previously admitted the party had a "mountain to climb" to overturn Mr Goldsmith's 23,000 majority from last year's election, but intends to battle him on a pro-EU ticket.
The former London mayoral candidate forced the contest by ditching the Conservatives to stand as an independent in protest over the decision to give the go-ahead to a new runway at Heathrow Airport.
Despite being cast from Government into the parliamentary wilderness after a hammering in the General Election last year, the Lib Dems were heartened by a strong performance in David Cameron's former constituency this month.
The party's emergence as Mr Goldsmith's main opposition was partly evidenced by a handful of prominent Labour MPs calling on their party not to field a candidate in the contest, to avoid the risk of splitting the vote.
Speaking outside Grey Court School in Richmond, where the Lib Dems unveiled her as their selected candidate, Ms Olney said she was confident she could overcome Mr Goldsmith's majority.
She told the Press Association: "I think on paper it obviously looks a bit daunting, but I think one of the things is that Mr Goldsmith isn't standing as a Conservative this time, so it remains to be seen how much of that support he carries with him as an independent.
"Secondly, we've just come from the most fantastic swing in Witney of about 19% and, with a similar size swing, we'd actually defeat Mr Goldsmith - we've got lots of reasons to be optimistic about our chances in this election."
She added: "We're really looking forward to this campaign, we're keen to get our messages out there in front of the voters and we hope that we can persuade them that they really need another Liberal Democrat MP."