El-Sissi's inauguration took place at the Supreme Constitutional Court in the Egyptian capital, Cairo, in a ceremony attended by royal representatives from several Arab countries and African leaders, among others.
The swearing-in confirms the 59-year-old el-Sissi in the position of head of state that he has held de facto for nearly a year after toppling President Mohammed Morsi.
El-Sissi won a landslide victory in May 26-28 presidential elections, receiving 96.9 percent of the vote. His only rival, leftist leader Hamdeen Sabbahi, managed to glean just three percent.
The election was criticized as invalid by the opposition, as the turnout was only around 50 percent.
He replaces interim President Adly Mansour, with whom he is to sign a document on the transfer of power, according to a statement from the presidency.
El-Sissi has been elected to a four-year term.
The election was boycotted by Morsi's now-outlawed Muslim Brotherhood, which has been subjected to a massive security clampdown.
Thousands of Morsi's supporters have been rounded up since July last year, when the army, then led by el-Sissi, ousted the Islamist president after widespread protests against his rule. More than 1,400 people have been killed in violence following Morsi's departure from power.
The crackdown on the Brotherhood seems likely to continue, with el-Sissi saying in a recent TV interview that the group would not exist in his era.
El-Sissi now faces the challenge of ending the turmoil that has ensnarled Egypt since a 2011 uprising that deposed the longtime strongman, President Hosni Mubarak.
In the run-up to the election, el-Sissi said that "national security" would have priority over democratic freedoms, and his opponents fear he may impose an autocratic regime worse than that of Mubarak, who ruled the country with an iron hand for almost three decades.
A retired field marshal, el-Sissi is the fifth Egyptian president to rise to the position from the army.
tj/pfd (dpa, AFP)