Islamist Mohammed Morsi has promised a "new Egypt" as he took the oath of office to become the country's first freely elected president, succeeding Hosni Mubarak who was ousted 16 months ago.
At his inauguration before the Supreme Constitutional Court in Cairo, the 60-year-old also became the Arab world's first freely elected Islamist president and Egypt's fifth head of state since the overthrow of the monarchy some 60 years ago.
He took the oath before 18 black-robed judges in the Nile-side courthouse built to resemble an ancient Egyptian temple.
"We aspire to a better tomorrow, a new Egypt and a second republic," Mr Morsi said during a solemn ceremony shown live on state television.
"Today, the Egyptian people laid the foundation of a new life - absolute freedom, a genuine democracy and stability," said Mr Morsi, a US-trained engineer from the Muslim Brotherhood, a fundamentalist group that has spent most of the 84 years since its inception as an outlawed organisation harshly targeted by successive governments.
Hundreds of soldiers and policemen guarded the building as Mr Morsi arrived in a small motorcade.
Several hundred supporters gathered outside the court to cheer the new president.
In a departure from the presidential pomp of the Mubarak years, traffic was only briefly halted to allow his motorcade through on the usually busy road linking the city centre with its southern suburbs.
Mr Morsi's inauguration signals a personal triumph. He was not the Brotherhood's first choice as president, and was thrown into the presidential race when the group's original candidate, chief strategist and financier Khairat el-Shater, was disqualified over a Mubarak-era criminal conviction.
Derided as the Brotherhood's uncharismatic "spare tyre", his personal prestige has surged since his victory and a speech yesterday which tried to present him as a candidate not just of Islamists but of all those who want to complete the work of the 2011 uprising against the authoritarian Mubarak.