France's foreign affairs ministry did not wish to make the French victim's identity public Saturday.
The train between the capital Yaoundé and the port of Douala, which was packed because of the collapse of a bridge on the road between the two towns, came off the tracks near Eseka, in the centre of Cameroon.
Rescuers on Saturday said that at least 73 people died in the crash and nearly 600 people were injured.
"I have learnt with sorrow of the tragic rail accident on 21 October," Ayrault said in a statement.
He pledged France's "full solidarity" with Cameroon, the victims and their families.