The Arab League is preparing for a two-day summit in Doha where opponents of President Bashar al-Assad will represent Syria for the first time.
Arab foreign ministers met in Doha on Sunday to prepare for the meeting, which begins in the Qatari capital on Tuesday.
Fighting in Syria and Afghan government peace talks with the Taliban will be high on the agenda at the summit.
One day after he announced his resignation, Moaz al-Khatib, the president of the Syrian National Coalition, has arrived in Qatar for the summit.
It was unclear whether al-Khatib still represented the SNC. The Syrian opposition group has rejected his resignation.
Stalled talks
Al-Khatib confirmed that he would address the summit, but he did not say when he would speak.
"I have decided to give a speech in the name of the Syrian people at the Doha conference," he wrote on his Twitter account.
"This is a matter that has nothing to do with the resignation, which will be discussed later."
The 22-member league suspended Syria after al-Assad's forces launched a bloody crackdown on dissent which has since turned into a civil war in which more than 70,000 people have been killed, UN figures show.
Al-Khatib was picked as head of the coalition after it was formed in November. He was seen as a moderate defender against the rising influence of al-Qaeda-linked forces fighting in the revolt against al-Assad.
Al-Khatib said in a written statement on Sunday that he was resigning so that he could work more freely.
In another Arab League summit first, Afghan President Hamid Karzai will discuss peace negotiations with the Taliban.
The breakthrough comes after years of stalled discussions with the United States, Pakistan and the Taliban.
King Abdullah of Saudi Arabia, a strong backer of the two-year-old Syrian rebellion, and Iraq's President Jalal Talabani will be absent from the summit for health reasons.
PHOTO CAPTION
Qatari Prime Minister and Foreign Minister Sheikh Hamad bin Jassim al-Thani (C), Arab League Secretary General Nabil al-Arabi (L) and Arab League Deputy Secretary-General Ahmed bin Helli attend a preparatory meeting with Arab foreign ministers ahead of the annual Arab League Summit in Doha, Qatar, 24 March 2013.
Aljazeera