The Arab League has given Syria's seat in the 22-member bloc to the opposition coalition at the opening of an annual summit in Qatar, DPA reported.
Qatar, a staunch supporter of the opposition, had invited members of the opposition National Coalition, to attend the meeting for the first time.
"I ask you to invite Ahmed Moaz al-Khatib and Ghassan Hitto ... to occupy the seat of Syria at this summit," Qatari Emir Hamad bin Khalifa Al Thani said in opening remarks.
Coalition leader al-Khatib led a small delegation into the hall to occupy the seat which has been vacant since the league suspended Syria's membership in November 2011.
The Syrian national flag was replaced with the green, white and black flag of the rebels - and which was used when Syria gained independence in 1946.
Al-Khatib said: "This seat is part of restoring the legitimacy that the Syrian people have lost long ago."
Syria criticized the handover, which comes at a time of deep divisions within the opposition.
Al-Khatib did not mention his desicion to resign at the weekend, instead expressing support for the opposition's recently elected premier, Ghassan Hitto, who sat behind him.
Some rebel groups have rejected the election of Hitto, who is believed to be backed by Syria's Muslim Brotherhood and by Qatar.
"We repeat that the people have paid the price of their freedom with their blood, and reject any (outside) power having authority over their decisions," al-Khatib said.
The opposition leader said he asked the United States to extend the use of Patriot missiles - deployed in Turkey to protect its airspace against Syrian attacks - to protect rebel-held areas in Syria.
"I have asked (US Secretary of State John) Kerry to extend the umbrella of the Patriot missiles to cover the Syrian north and he promised to study the subject," al-Khatib said.
The Syrian uprising started in March 2011 with peaceful protests against the rule of President Bashar al-Assad but quickly descended into a civil war that has claimed more than 70,000 lives, according to conservative UN estimates.
Al-Khatib also defended the presence of foreign fighters in Syria, accusing al-Assad's allies, Iran and the Lebanese Shiite movement Hezbollah, of sending militants to support the regime.
Turkish Foreign Minister Ahmet Davutoglu called for handing Syria's seat at the United Nations to the opposition.
"We must start working for the Interim Government to get its place at the United Nations," Davutoglu told the summit.
Iraqi Vice President Khodeir al-Khazaei told the opening session: "We reiterate our position of fully supporting the legitimate aspirations of the Syrian people and supporting a peaceful, political, Syrian solution ... without any interference."
The league's rotating leadership was passed from Iraq to Qatar.
"We are with the political solution, as long as it does not turn the clock backwards," the qatari emir said.
He also proposed a 1-billion-dollar fund for the preservation of Jerusalem. He said his country will contribute 250 million dollars.
He proposed to hold a mini-Arab summit in Cairo to speed up the reconciliation between rival Palestinian factions, Fatah and Hamas.
Sheikh Hamad also called on Arab nations to help Egypt overcome its economic difficulties. Qatar gave Egypt a 500-million-dollar grant and a 2-billion-dollar loan.
President Mohammed Morsi warned against foreign interference in the Egypt's affairs and vowed to respond firmly to any attempts at meddling.
"Egypt does not interfere in other countries' internal affairs ... so we do not accept anyone sticking his finger (in Egypt's affairs). It is forbidden," Morsi told the evening session.
Morsi, Egypt's first civilian and Islamist leader, faces a political crisis at home. The secular opposition accuses Morsi and his Muslim Brotherhood group of a power grab.
Sources at the summit said that Arab leaders will wrap up their meeting later on Tuesday, after it was originally scheduled to be held over two days.