The two-day meeting in the Spanish city of Cordoba on Thursday brought together members of the Western-backed National Coalition as well as delegates from opposition groups inside Syria that do not want removal of Syrian President Bashar al-Assad.
After nearly three years of deadly conflict, the opposition has fractured into competing groups with different regional backers.
Addition of extremist and foreign militant groups to the opposition has caused the group to lose popularity both among the Syrian people as well as some of their foreign supporters.
Prospects for progress at the peace talks dubbed the “Geneva 2” appear dim.
The opposition has been changing position from refusing to attend the talks to setting pre-conditions that are considered as red-lines for the government that it has said will never cross.
"Most colors from Syria are represented here," said veteran dissident Kamal Labwani at the meeting.
At least three members of the so-called Islamic Front had also come, he said. The front is made up of several extremist brigades which represent a large portion of militants on the ground and reject the authority of the National Coalition.
"We want them to be here. We will listen to them," Labwani said.
Diplomats say the gathering is recognition that the divided National Coalition - which has yet to formally accept an invitation to attend Geneva 2 - is losing influence on the ground and a more comprehensive grouping is needed ahead of the talks.
Militants from the Western-backed Free Syrian Army were also at the meeting in Cordoba, a venue chosen by the Spanish government because of its historical importance as the capital of the Islamic caliphate during the Middle Ages.
Organizers said they did not have a complete list of attendees and some unexpected delegates had turned up.
A representative from Liwa al-Islam, a brigade that works with the Islamic Front, told Reuters he was attending the meeting but gave no further details of his role.
The war in Syria started in March 2011, when pro-reform protests turned into a massive insurgency following the intervention of Western and regional states.
The unrest, which took in terrorist groups from across Europe, the Middle East and North Africa, has transpired as one of the bloodiest conflicts in recent history.
According to the United Nations, more than 120,000 people have been killed and a total of 7.8 million of others displaced due to the violence.
SHI/BA