Leave.EU co-founder Arron Banks will challenge former Ukip MP Douglas Carswell for his Clacton seat on the 8 June, a source close to Banks confirmed to IBTimes UK on Tuesday 18 April.
Banks, an ex-Ukip donor and Nigel Farage ally, clashed with Carswell during the former Conservative's time with the Eurosceptic party.
When Carswell quit Ukip, in the wake of Theresa May invoking Article 50 and starting two-year-long Brexit talks with the EU, Banks vowed to run against him as part of his new Patriotic Alliance movement.
'A million percent yes [he will still run],' a source close to the insurance millionaire told IBTimes UK. Banks plans to visit the seat on 20 April to kick off his campaign.
The move will come after the prime minister shocked Westminster and called a general election for 8 June. The Fixed-Term Parliaments Act 2011 means May will need a two-thirds majority from MPs to hold the snap ballot, but Labour leader Jeremy Corbyn and Liberal Democrat chief Tim Farron have already backed the election.
Carswell secured a majority of more than 3,000 votes over the Conservatives at the 2015 general election. He currently sits in the Commons as an independent MP.