A few weeks after his appointment as President of the SNC, he created a firestorm of controversy, bypassing the coalition by offering to negotiate directly with the Syrian government.
It was an initiative that the UN Envoy Lakhdar Brahimi called a "breakthrough". But al-Khatib’s appeal for talks with the regime ultimately went nowhere.
He continued his own campaign, going inside Syria to speak with people in the north, and videotaped singing with opposition fighters. No one could say he was “out of touch”.
But many in the SNC accused him of not being a team-player.
He spoke passionately at international conferences, critical of the world’s major powers for standing by while the Syrian people suffered.
But behind the scenes, he tells us, he was growing increasingly frustrated by the internal politics of the Syrian opposition.
“The people inside have lost the ability to decide their own fate," he says.
"Matters have now reached a point that it is no longer acceptable. I have become only a means to sign some papers while there are hands from different parties involved who want to decide on behalf of the Syrians.
“There are many things I do not agree with and there were ambiguous agreements that I think were not in the interest of the Syrian people.”
This weekend, he is formally resigning his post, but questions abound:
What really prompted him to step down? Who is now calling the shots? And how will he carry on his work?
This week, Talk to Al Jazeera sits down with Moaz al-Khatib, to find out his reasons for leaving, and how he is managing the current situation.