Jess Phillips is the latest to withdraw her bid for the top position, following Clive Lewis the week before.
Sir Keir Starmer is still the frontrunner followed close behind by Rebecca Long-Bailey, while Wigan MP Lisa Nandy has been labelled a "dark horse" in the race.
Ms Long-Bailey has been endorsed by a number of senior party figures, many of which want to see a woman as the next Labour leader.
Now, as the formal election process gets underway, the Standard takes a look at the remaining hopefuls and what they have to offer.
Who are the candidates in the Labour leadership contest?
Four Labour MPs remain in the leadership contest:
Sir Keir Starmer
The shadow Brexit secretary is the current front-runner for the Labour leadership, having entered the race on January 4 with calls to "rebuild" the party "fast".
The MP for Holborn and St Pancras said Labour had lost the public’s trust over a lack of clarity on Brexit, anti-Semitism, and a “feeling that the manifesto was overloaded”.
However, he told Andrew Marr that “we shouldn’t retreat from the radical” as he outlined his vision for the future.
Sir Keir is now the only man in the running, after his colleague Clive Owen dropped out early on.
Some senior Labour figures are hoping a woman to take up the role, with party chairman Ian Lavery urging Sir Keir to "stand down" in favour of his closest competition Ms Long-Bailey.
Despite this, Sir Keir is backed by two trade unions and has recently received the backing of Ms Phillips, ex-contender, who said Sir Keir is her second favourite to win behind Lisa Nandy.
The shadow business secretary, a key ally of Mr Corbyn, said the party needs a “proud socialist leader" driven by their principles and "unwavering determination" as she officially entered the race.
Ms Long-Bailey has assured voters that she would be taking the party "in a completely different direction".
She is backed by Labour's left, campaign group Momentum, trade union Unite the Union and senior Labour figures including Ian Lavery and John McDonnell.
Recently announcing her backing for an open selection process in the way Labour selects its parliamentary candidates.
Emily Thornberry made it through the first stage of the contest by a whisker, receiving 23 backers in total – just one more than the required 22 – with just minutes to spare before the deadline.
The 59-year-old, who was the first candidate to throw her hat into the ring, deputised for Mr Corbyn at Prime Minister's Questions, but was replaced after publicly calling for Labour to back another EU referendum.
She blamed her party's “dreadful” results in the election largely on its overly ambitious manifesto, saying it “just wasn’t convincing because their was too much in it”.
Wigan MP Lisa Nandy announced her candidacy in a letter to the Wigan Post on January 3. In it, she claimed to have "a deeper understanding of what has gone awry in our discredited political system" having represented her constituents since 2010.
She cited a lack of trust as the key factor in Labour’s defeat, blaming Mr Corbyn for failing to acknowledge the power of the Prime Minister’s Brexit message.
Through to the final round of the leadership contest, she has been described as the "dark horse" of the competition.
Recently, she has strongly voiced her concerns about New Labour's "Thatcherite consensus", accusing Tony Blair's government of continuing the late Tory Prime Minister's policies.
Jess Phillips backed Ms Nandy as her favourite to win after exiting the competition saying she could not unite the party.
Who has pulled out?
Birmingham Yardley MP Jess Phillips was one of the first of the five candidates to announce her bid. If elected, the backbencher represents a clean break from Corbyn-era politics.
She has already said she will not commit to re-nationalising all key utilities, adding that Mr Corbyn's free broadband proposal was "unbelievable".
Shadow treasury minister Clive Lewis pulled out of the race just an hour before nominations closed.
He announced his candidacy early, becoming only the second person to enter the contest behind Ms Thornberry, but managed to secure the backing of just five MPs.
After bowing out, Mr Lewis issued a statement urging the other candidates to be "strong enough" to take forward some of his policies and to be "radical, democratic, internationalist, green, open and pluralist".
Other MPs were touted for the top job, including shadow international trade secretary Barry Gardiner, former leadership candidate Yvette Cooper and party chairman Ian Lavery, but all ruled themselves out.
Who is currently favourite to win?
Sir Keir is the clear favourite to win the leadership race, according to both the bookmakers and a recent YouGov poll.
The survey showed that the shadow Brexit secretary would win 61 per cent of the vote in the final ballot.
Ms Long-Bailey comes in second with 39 per cent, according to the data.
Bookies have given Sir Keir odds of 2/5 to win, Ms Long-Bailey is 5/1, Ms Nandy 6/1 and Ms Thornberry behind with odds of 80/1.
Jess Phillips was predicted to survive the third longest in the race, getting knocked out with 18 per cent in the penultimate round. She has now quit.
What are the next key dates in the leadership race?
First-round nominations from MPs and MEPS close at 2.30pm.
January 14 - 16
Registered supporters who are not full party members have 48 hours, starting on Tuesday 14, to secure their vote by paying £25.
Nominations open for Constituency Labour Parties and affiliates.
Ballot opens for Labour party members, registered and affiliated supporters, with voters ranking candidates in order of preference.
Results are announced and the new Labour leader is declared.