President Nicolas Sarkozy's office said the soldier was a lieutenant from the 17th Parachute Engineering Regiment, based in the southwestern French town of Montauban, and that he was killed in Afghanistan's Kapisa province.
He was the 75th French soldier to die in Afghanistan since allied forces deployed there in late 2001 following the US-backed overthrow of the Taliban.
Defence Minister Gerard Longuet added that "several" more soldiers had been wounded in the battle, including "three more seriously than the others".
French military spokesman Colonel Thierry Burkhard said that a patrol of French and Afghanistan troops had been dispatched to search houses in an area from which rockets had been fired at their advanced bases in the region.
He said the unit had come under attack and had responded, killing five insurgents and capturing 10 in a series of clashes through the morning.
Around 4,000 French troops are based in the mountainous Kapisa region supporting the NATO-led effort to battle Taliban rebels and to build up and train the forces of Afghan President Hamid Karzai.
Polls show that French public opinion has turned decisively against the conflict, but Sarkozy has said he is determined to continue to support the mission until other NATO contingents leave in 2014.
Earlier, the French television network TF1 revealed that one of its reporters, Patricia Allemoniere, had been lightly wounded when the French patrol, which she was accompanying, was ambushed.
Burkhard confirmed that this was in the same incident as the deaths.
TF1 news editor Catherine Nayl said Allemoniere received treatment for superficial cuts to the face after she was caught by flying glass, and had been flown to a military hospital in a French base in Tagab.