UKIP leader Gerard Batten has stepped down after just over a year in the job.
He had said his position would be “untenable” if he lost his seat in European Parliament.
Party chairman Kirstan Herriot said “we are incredibly grateful to Gerard for his dedicated service to the party and expect to be announcing our new leader in early August”.
Mr Batten was elected unopposed in April last year, following the resignation of former leader Henry Bolton.
Deputy leader Mike Hookem quit his role last month and has announced he’ll run for party leader.
He said he could no longer support the party under Mr Batten’s leadership.
"Mr Batten's policy direction and associations have given the mainstream media the ammunition to label our party 'extreme' and 'far-right', accusations I do not believe to be true."
In April, Mr Batten defended an MEP candidate who wrote he “wouldn’t even rape” a Labour MP.
He said Carl Benjamin’s tweet was “satire”, and “he is not a bad person”.
UKIP won 24 seats in the 2014 European elections; however by 2019 most of these members had stepped down or defected to the Brexit Party.
The Brexit Party, led by former UKIP leader Nigel Farage, won 29 seats in last month’s elections.
UKIP won no seats.
The proposed date for the leadership results to be declared is August 10.
The new leader will be the party’s seventh in just under three years.