The Ukip MEP is expected to meet Michel Barnier in Brussels on Monday to discuss the UK’s departure process and the continuing wrangle over a trade deal.
Mr Farage, who heads a Euro-sceptic grouping in the European Parliament, requested the meeting after a string of British politicians including ex-Lib Dem leader Sir Nick Clegg and pro-Brussels Tory MP Kenneth Clarke.
In his letter to Mr Barnier, the former Ukip leader wrote: “As you appear to be conducting a series of meetings with UK political figures on the issue of Brexit, I wish to make a request.
“It seems that you are listening to a group of people who want to stop or delay Brexit.
“I will come to speak for the 17.4 million who did not vote for a transition deal or any further delays and whose resolve is getting stronger.”
The Open Britain pressure group, which is campaigning for the UK to keep strong links with Brussels, reacted angrily to news of Mr Farage’s meeting with Mr Barnier.
Open Britain executive director James McGrory said: “Sending Nigel Farage to Brussels to sort out Brexit is like sending an arsonist to put out a house fire.”
But former Labour prime minister Tony Blair, who is campaigning to try to halt Brexit, said: “People like Nigel Farage are entitled to say what they think.
“I’d like to be a fly on the wall in that meeting but yeah – why not, he’s perfectly entitled to see him.”
The revelation comes just hours after Mr Farage condemned the former prime minister for telling Britons it is not too late to reverse Brexit and calling for a second referendum.
The arch-Remainer said the decision to leave the EU would torpedo Britain’s remaining global clout and be regretted for generations to come.
Mr Blair, Labour prime minister from 1997 to 2007, said Britain would be poorer and weaker, and he warned Theresa May had solved none of the problems over Northern Ireland’s post-Brexit status.
The 64-year-old wrote on his website: “2018 will be the last chance to secure a say on whether the new relationship proposed with Europe is better than the existing one.”
And in an interview on Radio 4 he told John Humphrys Britain needed a second referendum because people “didn’t know what the terms of the new relationship will be”.
The ex-Ukip leader responded furiously to Mr Blair’s comments, writing on Twitter: “Wrong on the ERM. Wrong on the Euro. Wrong on Brexit!”