The Labour previously rejected the idea of holding a popular vote on the country's membership in the European Union in the run-up to the May 7 UK general election, which saw the Conservatives claim a majority in the parliament.
"The British people want to have a say on the UK's membership of the European Union. Labour will therefore now support the EU referendum bill when it comes before the House of Commons," Harman was quoted as saying by the Sunday Times.
Earlier this month, a spokesperson for Prime Minister Cameron said that the United Kingdom could hold an EU referendum before 2017.
The United Kingdom has been part of the European Union since joining the bloc in 1973, but has refused, alongside eight other countries, to replace its national currency, the pound, with euro.
Currently, the European Union comprises 28 member states.
