Lucy Harris, who was elected along with Jake Pugh and John Longworth in the summer, will this morning join Mr Longworth, Annunziata Rees-Mogg and Lance Forman in calling for voters to back the Tories if they want to get Brexit done.
It comes after the Brexit Party yesterday said Mr Longworth had "repeatedly undermined" its election strategy and withdrew the whip from him.
A statement issued by the Brexit Party's chief whip and MEP Brian Monteith said: "We regret having to remove the whip, but we have been left with no alternative after John Longworth repeatedly undermined the party's Brexit strategy over the last few months.
Mr Longworth told The Yorkshire Post yesterday: “The withdrawal of the whip is news to me as the Brexit Party didn’t have the courtesy to speak to me about it. I do not know what has precipitated this latest decision, I can only speculate that it may have something to do with a confidential vote in the EU Parliament.
"However, as the vote was taken in camera for timing reasons and I respect the rules of the Parliament I cannot comment further as it was a secret ballot. I will continue to fight for Brexit as an independent.”
Today he added: “For those who want Brexit, Boris Johnson’s deal is the only option available, Labour does not have a plan.”
Ms Harris said: “The Brexit Party has played an essential role in getting us to a point where Brexit can actually happen, now it’s time to get Brexit done.”
In a video released this morning the four urged voters to back the Conservatives in next week’s poll.
It leaves Mr Pugh as the only Brexit Party MEP left in Yorkshire.
A letter written by the four defecting MEPs to Brexit Party leader Nigel Farage said he was in danger of "putting Brexit in jeopardy" and said the party had "taken a wrong turn".
They said they were resigning the whip so there were "free to speak their minds" and the letter added: "It is unfortunate that as the race reaches the final straight our views on how best to achieve leaving the EU have diverged."
Mr Longworth has repeatedly clashed with leader Nigel Farage over the party's approach to Brexit and the election. The former director-general of the British Chambers of Commerce called on MPs to vote for Boris Johnson's Brexit deal despite his leader Mr Farage's stark criticism of the PM's proposals.
He has also called on the party to just stand 20 to 30 candidates, contradicting Mr Farage's position of opposing all sitting Labour MPs.
Yorkshire candidate in next weeks’ General Election wrote an open letter in response to today’s announcement.
In a letter signed by all the party’s Yorkshire candidates said: “Yorkshire's Brexit Party parliamentary candidates speak with unanimity and stand in support of our party leader and chairman.
“The Brexit Party strategy of fighting all the Labour heartland seats is the right one for the millions of Yorkshire's voters left politically homeless and democratically disenfranchised by Jeremy Corbyn and his party's betrayal of their vote to Leave the European Union.
“We will continue to represent those people's democratically expressed will and continue to work towards an independent UK, free of the EU's legal, military and restrictive economic institutions.
"With our strong, clear voice in our own Westminster parliament, those who continue to speak in the Brussels parliament for a different party's interests rather than the Brexit Party voters they were elected to serve will soon be sidelined and forgotten.
“The energy for the Brexit Party in Yorkshire is strong and growing fast. The Brexit Party is their party. We stand with our party and for the people we mean to represent. We stand united to deliver Brexit.”
Mr Farage said: "We are disappointed that four of our MEPs don't seem to understand that we both saved the Conservative party from large scale losses to the Liberal Democrats in the South and South West of England.
"We are also hammering the Labour Leave vote in its traditional heartlands making it much easier for the Conservatives to win many of those seats.
"The only vote on the Leave side that is currently being split is in areas such as Barnsley, the South Wales valleys, Doncaster and Hartlepool where there is a risk that the Tories will split our vote."