Mohammed Morsi has been declared the first president of Egypt since a popular uprising ousted Hosni Mubarak, the head of the electoral commission has announced.
Mr Morsi, who ran against ousted leader Mubarak's ex-prime minister Ahmed Shafiq, won 51.73 per cent of the vote after a race that polarised the Arab world's most populous nation.
Mr Morsi resigned from his posts in the Muslim Brotherhood and its Freedom and Justice Party, which he headed, after he was declared the winner, the Brotherhood announced.
Thousands of Mr Morsi's supporters cheered in Tahrir Square following the announcement.
The June 16-17 runoff vote between Mr Morsi and Mr Shafiq left Egyptians with nerve-wrecking uncertainty as both candidates claimed victory and the results were delayed.
Both candidates rallied supporters to the streets in a show of strength amid speculation about last-minute backdoor deals between the powerful ruling generals and the rising Islamists over power-sharing arrangements.