Emmanuel Macron is to become the next president of France after winning a projected 65% of the votes, exit polls show.
French polling agencies showed the centrist candidate has triumphed over the far-right’s Marine Le Pen.
The National Front leader is forecast to have won just 35% of the votes.
Theresa May was quick to congratulate Mr Macron on his victory.
A Downing Street spokesman said: “The Prime Minister warmly congratulates President-elect Macron on his election success.
“France is one of our closest allies and we look forward to working with the new President on a wide range of shared priorities.”
Ms Le Pen, who had hoped to capitalise on the disillusionment of voters in France, said she had called Mr Macron to congratulate him on his victory just minutes after the polls came in.
French Prime Minister Bernard Cazeneuve said the vote was a rejection of the “deadly project of the extreme right”.
Outgoing president Francois Hollande congratulated Mr Macron and said his victory shows the overwhelming majority of voters rallied behind the European Union and openness to the world.
It was Mr Hollande who first brought Mr Macron into the world of politics, naming the untested ex-banker as economy minister.
But Mr Macron left the position to found his own political movement last year, and has distanced himself from his former mentor.