David Cameron has pledged to work "very closely" with Francois Hollande in a phone call to congratulate the new French president after he swept to power.
The Socialist leader defeated Nicolas Sarkozy after railing against austerity plans and threatening to block planned EU fiscal measures unless new growth measures are secured.
The Prime Minister did not meet Mr Hollande when he visited Paris in February and had indicated his support for Mr Sarkozy in the contest but the pair have agreed to build on the already "very close relationship" between the two nations.
A Number 10 spokeswoman said: "The Prime Minister called President-Elect Hollande this evening and congratulated him on his victory. They both look forward to working very closely together in the future and building on the very close relationship that already exists between the UK and France."
In his victory speech Mr Hollande said he was "proud to have been capable of giving people hope again".
Labour leader Ed Miliband said: "I congratulate Francois Hollande on his election as President of France.
"I know from our conversations in London earlier this year and from his victory speech tonight of his determination to help create a Europe of growth and jobs, in a way that is responsible and sustainable.
"This new leadership is sorely needed as Europe seeks to escape from austerity. And it matters to Britain.
"In his own campaign, he has shown that the centre-left can offer hope and win elections with a vision of a better, more equal and just world.
"I look forward to working together with him in the months and years ahead."