The 49-year-old Conservative leader had initially said he would continue as an MP until the next general election.
Outgoing British Prime Minister David Cameron on Wednesday said that post-Brexit the United Kingdom should "try and be as close to the European Union as we can be".
Millions voted in the United Kingdom on Thursday in the country's closest polls in decades as Prime Minister David Cameron's Conservative Party and opposition Labour were locked in a dead heat electoral battle with migrant voters, including the Indian diaspora, expected to be the deciding factor.
David Cameron, who became Britain's youngest prime minister since 1812 when he won elections in 2010, on Friday surprised everyone by securing a majority for the Conservatives against all odds to allow his party to govern alone for the first time in more than two decades.
Opinion polls have suggested that while big business is broadly in favour of staying in the EU, small firms have been evenly split in what looks like a photo-finish.