Farage – a two-time leader of UKIP – brought the party into the mainstream and was a leading figure of the Brexit camp during the EU Referendum.
The MEP has since clashed with the party's leadership as he voiced concerns over the direction of the party, in particular efforts to woo EDL founder Robinson.
Writing his resignation letter in the Telegraph, he blamed the party for trying to bring in "extremists" and warned this would "damage the party beyond repair".
He said: "With a heavy heart, I am leaving UKIP. It is not the Brexit party our nation so badly needs."
The 54-year-old was a founding member of UKIP after quitting the Tories, serving as an MEP since 1999 and having two stints as leader between 2006 and 2016.
“There is a huge space for a Brexit party in British politics, but it wont be filled by UKIP”
He said: "We are now just a few days away from the most ill-judged political event I have ever been aware of in British politics.
"The very idea of Tommy Robinson being at the centre of the Brexit debate is too awful to contemplate.
"And so, with a heavy heart, and after all my years of devotion to the party, I am leaving UKIP today.
"There is a huge space for a Brexit party in British politics, but it wont be filled by UKIP."
UKIP: Nigel Farage has quit the party over its wooing of Tommy Robinson (Pic: GETTY)
Farage last month said he was "appalled" after Robinson – real name Stephen Yaxley-Lennon – was appointed as UKIP leader Gerard Batten's special advisor on grooming gangs and prisons.
Robinson almost scuppered the trial of a notorious Huddersfield gang – who ended up being jailed for 221 years – when he was accused of violating contempt of court laws.
The ex-UKIP chief accused Batten of dismantling the party's reputation as a “non-racist, non-sectarian party” that talks about immigration and “extreme forms of Islam” by embracing Robinsons views.
Batten, who was elected UKIP leader in February this year, said Robinson has “great knowledge” about grooming gangs and prisons – the subjects he has been employed to advise on.
CONTROVERSIAL: Tommy Robinson has been welcomed into UKIP by its new leadership (Pic: GETTY) Related Articles
NEW DIRECTION: Gerard Batten has appointed Tommy Robinson his special advisor (Pic: GETTY)
Farage gave a speech at the Annual UKIP Conference in Birmingham, which he wrote in his column will go down as his last speech to the party.
The arch-Brexiteer – who once received hero worship from the membership – recalled he was confronted "several angry young men, red in the face and mildly abusive, who all seemed to be obsessed with Islam and Tommy Robinson" as he called for UKIP to detach itself from extreme views.
He wrote: "My heart sinks as I reflect on the idea that they [Robinson and his entourage] may be seen by some as representative of the cause [Brexit] for which I have campaigned for so much of my adult life."
His departure from the party comes as Britain braces itself for Prime Minister Theresa May to present her Brexit deal with the EU to Parliament in a make-or-break vote.
BREXITEER-IN-CHIEF: Nigel Farage was the leading voice in getting Britain to leave the EU (Pic: GETTY)
UKIP have seen their support base collapse following Britain's vote to leave the EU – and the party have only ever won one seat in the House of Commons.
Under the pro-Brexit platform of Farage the party won 3.8 million votes and fielded 614 candidates during the 2015 General Election.
And in 2017, the party only won 594,000 votes as it fielded just 378 candidates – its worst performance in an election since 2001.
Farage's exit came after UKIP veteran Suzanne Evans quit the party on Monday, citing the “perverse direction” being taken by Batten.