France was an Allied nation. However, they were quickly conquered in 1940, so didn't play much of role as a nation. After the Germans took over, they divided the country into two parts, the south part was theoretically still independent, but the Vichy government was basically a puppet government and did what ever the Germans wanted. Later, the Germans abandoned the pretense and just took control directly.
The French leaders in exile, mostly military leaders, were not a very unified lot. In fact there was much infighting to determine who would lead France after the war. Kind of sad really, but many of the French leaders were just looking out for them selves, or refused to openly support the Allied cause until they knew they'd win.
There was one French armored division that I know of deployed during the liberation of France, but there record was not spectacular.
So, basically, they were on the side lines officially, because they were occupied by the enemy.