Emmanuel Macron is to become France's next president after winning a projected 65% of the votes.
French polling agencies revealed the centrist candidate triumphed over the far-right's Marine Le Pen, who is forecast to have gained a 35% share.
The National Front leader called Mr Macron to concede defeat and congratulate him on his victory just minutes after the result came in.
Mr Macron - who at 39 will become France's youngest president - dashed Ms Le Pen's nationalist hopes with his pro-European stance and moderate policies.
In a sombre speech following his victory, the president-elect acknowledged divisions in society had driven people to "vote to the extreme" but said "a new page" of France's history was opening.
Theresa May was quick to offer her congratulations to Mr Macron.
In a phone call, the pair "briefly" discussed Brexit and the Prime Minsiter "reiterated that the UK wants a strong partnership", Downing Street said.