The former Tory prime minister spoke at a private lunch in Dallas, where he told US right-conservatives to “stick with it” and insist they were “backing the right horse” by supporting Ukraine.
“I just urge you all to stick with it – it will pay off massively in the long run,” Mr Johnson told the audience, according to Politico.
The ex-PM added: “You are backing the right horse. Ukraine is going to win. They are going to defeat Putin.”
Mr Johnson is said to have “gently mocked” Macron with a faux-French accent as he quoted his remarks about not wanting the Russian president Vladimir Putin “humiliated”.
“I think it was my French friend and colleague Emmanuel Macron who said ‘Putin must not be humiliated,’” he told the group of Republican politicians and donors.
“I think it takes an awful lot to humiliate Vladimir Putin, frankly,” he added. “I don’t think it’s our job to worry about Vladimir Putin’s ego, or his political prospects, or developments in his career.”
Mr Johnson called Mr Macron “Putin’s lickspittle” after the French president criticised the then-prime minister’s response to the Ukrainian refugee crisis, according to a former leading No 10 official.
Mr Johnson also called Mr Macron a “four-letter word that begins with c”, former director of communication Guto Harri said in his podcast Unprecedented.
Donald Trump and Florida governor Ron DeSantis, two of the leading candidates for the Republican nomination, have shared their scepticism about support for Ukraine.
But Mr Johnson told Republicans that had “every hope that the Ukrainians will be able to deliver a very substantial counterpunch this summer”, adding that there was “a prospect of a complete Russian military collapse”.
Joe Biden told fellow leaders at the recent G7 conference that the US would support providing fighter jets, including American-made F-16 jets.
Ukrainian president Volodymyr Zelensky called the decision one that would “greatly enhance our army in the sky.”
Mr Johnson has made around £5m from outside earnings in the past year, mostly from the lucrative speaking circuit, on top of the £84,000 salary he still receives as a backbench MP. But he is not believed to have been paid for the speech in Dallas.