Sarkozy held a 40-minute telephone conversation with Syrian National Council chief, Abdel Basset Sayda, a joint communiqué revealed on Tuesday.
The two expressed "complete agreement" on the serious nature of the Syrian crisis and the need for "speedy action by the international community", it said.
They also agreed that there was "great similarity" to events in Libya that led to the downfall of Moamer Kadhafi, an outcome that Sarkozy regarded as a triumph for his intervention in the conflict there.
Previous French presidents have usually refrained from involvement in foreign policy when their terms in office were over.
Sarkozy's communiqué is unlikely to please the present Socialist-led government, which is taking its own inititatives, although its policy in the Middle East is not markedly different to Sarkozy's.
Sarkozy declared that he was retiring from public life after his election defeat.