CAIRO – Egypt’s electoral commission announced Sunday that Muslim Brotherhood candidate Mohamed Morsi would be sworn in as president, becoming the Arab world’s first elected Islamist head of state after more than a year of popular uprisings that ousted autocrats and fueled the rise of political Islam in the region.

Egypt’s ruling generals blunted the power of the presidency shortly after polls closed last weekend, making Morsi’s victory partly symbolic. But the win represented a remarkable turn of fortunes for an organization that was outlawed and systematically suppressed for decades, including under the three-decade regime of deposed former President Hosni Mubarak.

Election officials said Morsi beat former Mubarak Prime Minister Ahmed Shafiq, whom he had faced in a runoff. Presidential election commission chief Farouk Sultan said Morsi won by a slim margin, winning almost 52 percent of votes cast.

Egypt’s presidential election commission had been expected to announce the winner Thursday, but the proclamation was delayed, Sultan said, because of a meticulous review of complaints of election violations. Those complaints included reported attempts to prevent Christians from reaching polling stations and fraudulent ballots.

As soon as the news of Morsi’s victory broke Sunday, Brotherhood supporters in Tahrir Square erupted in cheers and fired off firecrackers. Egyptians flooded in on foot, motorcycles and in cars. Morsi supporters embraced and danced to an near-deafening soundtrack of honking and cheers and euphoric crowds shouted “Down with military rule!”

Even those who were lukewarm to Morsi were excited that the country had had a free vote.

A Morsi loss could have generated serious political instability; Brotherhood supporters had vowed to continue their demonstrations if that was the outcome, saying it would have amounted to electoral theft.

Not long after he was declared the winner, the Brotherhood’s official Twitter account tweeted that Morsi had begun “talks to form his presidential team and a new cabinet that will truly represent Egypt after revolution.” Morsi had sought in recent days to gain the confidence of liberal and secular factions, promising a “broad coalition government” that would preserve the rights of women and Christians.

The Muslim Brotherhood said Sunday that Morsi had resigned from the organization and its political party, in line with a campaign pledge to remain independent.

But the terms under which Morsi will hold office, and the sway his Islamist supporters will have, remain uncertain. Sunday’s announcement capped a week of intrigue and rumors about whether the country’s ruling generals were seeking to broker a power-sharing deal with the Brotherhood before signing off on the 60-year-old group’s electoral victory.

Morsi’s election is sure to viewed as an inspiration to other Islamist movements in the Muslim world. It is also likely to be viewed as a potential threat by Israel, which depended on the Mubarak regime to adhere to a 35-year-old peace treaty between the two countries, and with skepticism by some secular, female and Christian Egyptians.

Conversely, it could buoy Hamas, the militant Islamist group that rules the Gaza Strip and is an offshoot of the Brotherhood. Hamas officials are hopeful that an Islamist president will lead Egypt to reconsider the peace treaty and to allow goods to be traded across the Gaza-Egypt border.