"Britain lived in equilibrium in the European Union… And now it is becoming a vassal state, ‘junior’ partner of the United States," Macron said.
UK Prime Minister Theresa May is visiting Washington on Friday. She met with US President Donald Trump, becoming the first foreign leader to be welcomed in the White House.
The United Kingdom is preparing to trigger Article 50 of the Lisbon Treaty, to begin its withdrawal process from the European Union, by the end of March.
Macron, who is running as the presidential candidate from the liberal En Marche! movement in the upcoming presidential elections, is now the third man in the race after National Front leader Marine Le Pen and right-wing Francois Fillon, polling at some 17-21 percent.