Mohammed Morsi, the Muslim Brotherhood leader once jailed by ousted dictator Hosni Mubarak, succeeds him as president of the world's most populous Arab nation.
Finally and officially on Sunday afternoon the election commission chief Farouk Sultan announced that Mohammed Morsi won 51.73 percent of the vote in the June 16-17 presidential runoff to beat Ahmed Shafiq, former military officer and Hosni Mubarak's last prime minister, who had 48.27 percent.
The US-trained engineer's victory in the country's first free presidential election breaks a tradition of domination by the armed forces, who have provided every Egyptian leader since the overthrow of the monarchy 60 years ago.
Mr Morsi will not enjoy the far-reaching powers exercised by Mubarak - those have been curtailed by the military establishment, who will remain a powerful force.
The Egyptian army is still effectively in charge of the country. The new president is not Egypt's commander in chief, is not in control of the budget or the writing of a new constitution. There is no parliament to support or oppose his democratic mandate.
"I tell everyone on this great day, that with your will I became a president for all Egyptians," Morsi said in a speech broadcast by state television late Sunday, as he tried to reassure women, Christians and those who did not vote for him.
Mr Morsi's narrow victory suggests that Egypt is a nation that is anything but united around the idea of Brotherhood rule. Mr Morsi won a little less than a quarter of the first-round vote in May.
US President Barack Obama congratulated Morsi by phone on Sunday, and also called the Islamist's defeated rival, Ahmed Shafiq, to encourage him to stay active in Egyptian politics, the White House said. Morsi was educated in America and worked as an academic in California. His children are US citizens.
Meanwhile British Foreign Minister William Hague hailed a "historic moment" for Egypt as Morsi was elected president.
European Union foreign policy chief Catherine Ashton described the election as a major milestone in Egypt's democratic transition and a historic moment for the country and the region. She encouraged Morsi "to reach out to all other political and social groups," the EU said.
French President Francois Hollande said he hoped that Egypt's transition would continue toward "a democratic and pluralistic political system and a state subject to the rule of law."
In the Gaza Strip, the Islamist movement Hamas, an offshoot of the Muslim Brotherhood, also celebrated the election results.
The Brotherhood's manifesto for an Egyptian renaissance with an Islamic foundation sketches out the group's vision on everything from fighting inflation to a reset of relations with the United States to a more equal partnership.
jm/ccp (Reuters, AP, AFP)