Rejoining the military command would allow France to make key planning decisions within the alliance and put French officers in charge of command posts.
"We want to take our place where the future of Nato is discussed," Fillon said.
Charles de Gaulle, the former president, pulled France out of Nato's military command in 1966, with the aim of seeking a less US-oriented policy during the Cold War.
Sarkozy has said it is time to climb back into Nato's sphere of influence, arguing that the end of the Cold War and cross-border threats have heightened the need for international military co-operation.
But the prospect has ignited fierce debate in a country that has long taken pride in setting its own diplomatic and defence direction.
"Our nation doesn't take orders from anyone," Fillon said in defending the move.
"France will remain France, with its demand for truth and its demand for grandeur."
Herve Morin, the defence minister, told Reuters news agency on Tuesday that given France's role as a major Nato contributor, it made sense for it to actively participate in the military planning process
European arms manufacturers also hope the move will give them a boost over US competitors by shifting the balance within Nato towards Europe.
Nato officials have welcomed the prospect of using France's expertise in the military planning process.
However, France will not join Nato's nuclear planning group and will keep its nuclear force independent.