Haitham Maleh, a member of the executive committee of the Syrian National Council, told The Daily Telegraph that Mr Assad had forfeited any chance of a peaceful exit from Syria as a result of his regime's brutal crackdown on protesters.
The former judge, who has spent decades in Syrian prisons for his human rights activism, predicted that Mr Assad, his wife and three children would be killed in revenge for his failure to respond positively to peaceful demands for change.
"Assad and his family will be killed in Syria, their next steps will be very bloody," he said. "Two months ago we offered him the option to leave us alone and go but instead he went for the blood of his people. The end for him will be that he is killed like Gaddafi."