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.
In his first public speech at Cairo University after the oath, Mursi said, “God is greatest, above everyone” and pledged that Egypt would not reverse its new democratic course after Hosni Mubarak's fall.
Egypt's president stressed on a Pan-Arab policy and also announced his support for the Palestinians until they “regain all their rights” and called for an end to bloodshed in Syria.
“I announce from here that Egypt, its people and presidential institution stand with the Palestinian people until they regain all their rights,” Mursi said. “We support the Syrian people. We want the bloodshed to stop,” he added.
Mursi thanked the military for seeing through the presidential elections but pointedly mentioned the “elected parliament” several times, in the address.
“The elected bodies will resume their functions and the army will return to their barracks, to their original role of protecting the borders,” Mursi said sending a veiled message to military's leader Field Marshal Hussein Tantawi who was among the audience.
As the families of those who died during this year of revolution cheered for Mursi, holding pictures of their children, the president addressed them, saying: “It's because of the sacrifice your children made that we have all of this.”
Mursi promised to bring justice for the martyrs and injured, for many have neither received any benefits from the state nor have they seen their murderers given jail sentences.
Mursi also expressed his appreciation to the role played by judges, the armed forces and police officers for supervising and securing the elections process and ensuring its transparency.
“Egypt will not break away from the Arab and Islamic nation,” said the president, stressing that from now on Egypt will not tolerate any violations against any of the Arab countries.
Attempts by any country to intervene in Egyptian affairs will be rejected, and confirmed that Egypt will respect “international treaties and agreements,” which might be an indirect reference to treaties such as the Camp David Accords.
The president reached out to both Muslims and Christians in “drawing a better future for Egypt and in fulfilling the goals of the revolution: freedom, social justice and dignity.”
“It's time to look forward to a prosperous future for Egypt,” said the president before leaving the podium amidst cheers.
Earlier today 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.
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 said a civilian and constitutional state had been “born today,” in his comments after swearing 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.
Mursi is facing a very tough challenge as the military generals who ruled the country after former President Hosni Mubarak stepped down have already curbed his powers.
Many political forces had called on Mursi to refuse to take the oath before the SCC, saying that doing so means accepting the controversial complementary constitutional declaration the ruling military council issued this month curbing his powers.
But legal experts warned that if Mursi refused to take the oath, he would be acting against the country's formal legal measures.
The Islamist, in a suit and burgundy tie, promised to lead a “civil, constitutional and modern state” in a short speech after taking the oath.
“We aspire to a better tomorrow, a new Egypt and a second republic,” Mursi said.
Mursi, was forced to take his oath at the court instead of in parliament after the military disbanded the Islamist-led house following a court order earlier this month.
Mursi arrived in a small motorcade as several hundred supporters gathered outside the court to cheer the new president.
His rise to presidency marks a dramatic reversal of fortunes for the Brotherhood that was banned under ousted leader Hosni Mubarak.
Mursi, in his first public speech yesterday promised to be a “president for all Egyptians”, adding: “You are the source of all authority and legitimacy.”