The party formed a coalition government with the Conservatives under David Cameron in 2010, but was nearly wiped out in the 2015 general election.
Zac Goldsmith has been unseated in a stunning by-election upset by the Liberal Democrats.
He ran as an independent candidate after quitting the Conservative Party over the government's decision to expand nearby Heathrow Airport.
Goldsmith's strengths were his massive local popularity - turning what was a Lib Dem seat until 2010 into a 23,000 Tory majority by 2015 - and his principled stand over a third runway in a constituency already marred by aircraft noise.
Lifelong Labour voter William Palmer, 71, said he would vote Liberal Democrat on Thursday, and that Labour fielding a candidate was "absolutely pointless" in Richmond Park.
To her rival Mr Goldsmith, she said: "I wish you well and assure you I will continue your fight against the expansion of Heathrow".
"In Witney we had to spend the first couple of weeks establishing ourselves as the main challenger - here people will see from the get-go that we are the only challenger to the Conservative Brexit Government, and we are determined to put in an extremely strong challenge for this seat".
Olney's campaign was supported by the Green and Women's Equality Party among others. A year and a half ago, their man won by almost 40% and had a majority of more than 20,000.
Ms Olney said the result was a rejection of the "politics of anger and division", and dissatisfaction with the way Brexit was being handled.
Before being elected to her new role in Parliament on Friday, she worked as an accountant for the National Physical Laboratory - which specialises in measurement - in Bushy Park. She lives in North Kingston with her husband Ben and two children.
The Lib Dems say a shock result would force the government to think again about pursuing a so-called "hard Brexit" divorce from the European Union.
"I will do all I can to make sure of it".
She said: "I think the Labour vote in Richmond has proved very resilient in the past, and I think it will be resilient again".
She shares Mr Goldsmith's views on Heathrow, opposing the building of a third runway at the hub.
This is the second election that Goldsmith has lost this year, after he was defeated by Sadiq Khan for the London mayoralty in May.
The polls have just closed in Richmond Park and counting is about to begin. Sky News reported that this is the highest in a United Kingdom mainland by-election since the Conservatives won Crewe and Nantwich from Labour in 2008.
The second leg of the Brazilian Cup final between Atletico Mineiro and Gremio was one of the games postponed until next week. The capital Bogota was mentioned on the flight plan as a possible refuelling stop, but the plane did not land there.
The news Halo Wars: Definitive Edition would be bundled with Halo Wars 2: Ultimate Edition was revealed at E3 2016 in June . People who pre-order the Ultimate Edition will receive early access to the Definitive Edition starting December 20.
Two Upstate law offices have come together to represent Kala Brown in filing civil suit against her alleged captor Todd Kohlhepp. For those interested in supporting Kala Brown's recovery efforts, please visit www.KalaBrown.com to make a donation.
She also won the Women's Tennis Association's most improved player award for 2016, having been ranked 147 in June 2015. Johanna Konta has surprisingly split with her coach Esteban Carril after breaking into the world's top 10 in 2016.
They are also looking into a Facebook post allegedly written by him from that same morning about USA interference in Muslim lands. Artan called al-Awlaki a "hero" in a Facebook message US investigators believe he posted under a slightly different name.
Yesterday, fellow VS model Kelly Gale thought it'd be fun to do some filming on the Angel's plane as she stood right behind Bella. Speaking before the event began, she added to Elle .com: "I couldn't sleep - I was so excited last night and kind of jet lagged".
They were also believed to be newly displaced from the government onslaught on the northern parts of eastern Aleppo . Regime forces were fought off Sheikh Saeed district in the south of the city on Wednesday.
It was the most audacious attack on an Indian military base since a September 18 assault at an army base in the town of Uri. Seven Indian soldiers, including two officers, were killed when armed men attacked an army base in Indian-occupied Kashmir.
The order for a December 5 hearing came a day after the campaign of failed Green Party candidate Jill Stein filed the request. Many of Hillary Clinton's supporters have given their backing to the Green party candidate's fundraising efforts.
Minnesota sits effectively two games back of Detroit after surrendering the tiebreaker to their Thanksgiving opponents last week. That game was notable becaue the Eagles took a 17-0 lead in the first quarter, then the Raiders scored the last 48 points.
The game follows the story of Grayson Hunt, a professional assassin who's been exiled from the elite group Dead Echo. Called Bulletstorm: Full Clip Edition , it will be available on PlayStation 4, Windows PC and Xbox One on April 7.
His staff said he spent much of the Thanksgiving break making calls to his colleagues and they believed it would be a close race. Pelosi had publicly predicted that she had support from two-thirds of the caucus, a threshold she surpassed in Wednesday's vote.
Chapecoense air crash: Colombia investigates fuel link
Only six people of the 77 on board survived the devastating crash in La Union town, outside of the north-eastern city of Medellin. A Brazilian defense ministry spokesman said 20 bodies had been identified by Wednesday morning.
Delhi Police files FIRs — Rahul's Twitter hack
During the meet, Gandhi even pointed out that there is an increase terror attack and ceasefire violations. Congress Parliamentary Party meet which was being chaired by Rahul Gandhi for the first time, ends.