Mr Woolfe abandoned his bid to become leader of the party, claiming it was “ungovernable” without Nigel Farage leading it, and the European Union referendum cause to unite behind.
He stood by his claim that he had “received a blow” from Ukip MEP Mike Hookem during the fracas at a meeting in Strasbourg which caused the injuries leading to him requiring hospital treatment.
Mr Hookem has denied striking Mr Woolfe, and published photos of his hands in an effort to clear his name.
Mr Woolfe said he would continue sitting as North West MEP as an independent.
His announcement came after Ukip said its new leader would be announced on November 28.
Mr Woolfe said: “The events at the meeting in Strasbourg led to me later being treated by doctors for two seizures, partial paralysis and loss of feeling in my face and body.
“I would like to thank all of the medical staff in Strasbourg for their impressive and swift treatment. I owe them my life. I would also like to thank my family and friends for their love and support - and also all of the people in politics who have sent me their best wishes.
“Since then, I have spent some time considering my personal and political future.
“It is with deep sorrow and regret that I am aborting my leadership campaign and announcing my resignation from Ukip with immediate effect.”
He added: “With regards to the highly-regrettable events in Strasbourg, I will reiterate my position that I received a blow from Mr Hookem that knocked me back into the meeting room and caused my subsequent injuries. Contrary to reports, I have made a police complaint.
“I am now seeking legal advice in respect of the investigations and will not be commenting further on the matter until the completion of those investigations.”
Mr Woolfe had been seen as frontrunner in the race to replace Diane James, whose term as leader lasted just 18 days.
But the row with Mr Hookem, and his subsequent decision to quit Ukip, adds to the turmoil in the party.
In his resignation statement, Mr Woolfe painted a bleak picture of the state of the party, which is currently back under the control of Mr Farage as interim leader.
“I have come to the conclusion that Ukip is ungovernable without Nigel Farage leading it and the referendum cause to unite it.
“The way I was treated by members of my own party during the summer’s leadership campaign and the events that have led up to today have all contributed to me coming to this conclusion.
“The party is riddled with infighting, proxy wars between rival camps and is run by an NEC (national executive committee) that is not fit for purpose.”
Nominations to replace Ms James close on October 31.
All candidates will need 75 signatures from at least 10 branches to be eligible.
Candidates will also need to pay a deposit of £5,000 which shall be refunded upon polling at least 20% of the vote, while 80% will be returned if they withdraw by November 7.
There will be a series of hustings in the first two weeks of November, with ballots sent out to members on November 11.
The rules could clear the way to former deputy chairman Suzanne Evans standing in the election, after she was deemed ineligible last time because she had been suspended.
Under the terms of the contest all members who have been in good standing for 28 days are eligible to stand.