The Brexit Party leader paid tribute to Mr Johnson as “the man that finished the job” of delivering the UK’s exit from the EU and negotiating broadly agreeable terms for the two sides’ future relationship.
Sounding a warning note over fisheries, Mr Farage warned that the Prime Minister risked being judged “a little more harshly” by history if he has ceded too much access to UK waters for European boats.
Fish quotas were among the final points of dispute that Lord Frost, the UK’s chief negotiator, and Michel Barnier, his EU counterpart, were still wrangling over before the deal was signed off.
Mr Farage said that while the deal was “not perfect”, Mr Johnson has “done what he said he’d do on the big picture”, concluding: “On the big stuff, the war is over.”
The surprise endorsement, which came before the deal was secured and the 2,000-page legal text formally published, will reassure the Government that its trade agreement is unlikely to meet major resistance from Brexiteers.
Downing Street is understood to have briefed senior pro-Leave Tory MPs about the terms of the pact in a bid to ensure their support and avoid public criticism.
Mr Farage’s intervention marked the second time he has offered assistance to Mr Johnson after agreeing not to stand Brexit Party candidates in Conservative-held seats at the general election last December.
Writing on Twitter on Thursday morning, he paid tribute to the Prime Minister and Michael Gove, the Cabinet Office Minister.
They were “the two senior Conservative politicians who when the referendum came, albeit late in the day but that’s not the point, they had the guts to back Brexit and thank goodness they did”, he said.
He added: “So yes, Boris will be seen as the man that finished the job. Perhaps not perfectly, but yes he’s done what he said he’d do on the big picture. I suspect on some of the detail, such as [whether] we’ll be back in charge of our fisheries, history may judge some of those aspects a little more harshly.
“But on the big stuff, the war is over. It has gone on for decades in this country, from the Maastricht rebellion onwards, it’s never, ever gone away, the fight over whether we should be part of the European structures or not.
“And now we’re out and, arguably, with a new treaty that’s a bit close to a partnership agreement. It’s not perfect, but my goodness it’s still progress.”