Mursi, who was the winner of the presidential run-off, was officially sworn in before Egypt's High Constitutional Court as Egypt's first civilian president.
"I swear by the Almighty God to sincerely preserve the republican order and to respect the constitution and law, and completely care for the people's interest," 60-year-old Mursi said at the ceremony in the Constitutional Court.
"We aspire to a better tomorrow, a new Egypt and a second republic," Mursi said.
He became 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 his oath before the general assembly of the High Constitutional Court, composed of 18 top judges, lead by Farouk Sultan.
The ceremony was broadcast live by state television, after an apparent change of plans: state television had earlier announced the ceremony would be recorded and aired at a later time. The national anthem played to mark the beginning of the ceremony, with Mursi sitting between Sultan and his deputy judge, Maher El-Beheiry.
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Farouk Sultan congratulated Mursi on behalf of the judges' general assembly in an opening speech ahead of the oath-swearing.
"May God assist you with the challenging task you are taking on," said Sultan, adding that "based on article 30 of the Constitutional Declaration announced on 17 June 2012 I call you to swear the oath." Following Sultan's speech, Mursi recited the oath.
Mursi symbolically swore himself in yesterday before tens of thousands of supporters in the iconic Tahrir Square and vowed to fight for authority, defying country's ruling generals.
After the swearing in ceremony today, Mursi headed to Cairo University to give his first presidential address. MORE