Cyrille Hugodot was shot by an insurgent while carrying out an operation in the northeastern Kapisa province. He is the 63rd member of the French contingent to die there since 2001.
His unit was providing protection to engineers searching for improvised explosive devices (IEDs) at the side of the road, spokesman Colonel Thierry Burkhard said.
Hugodot had died of his injuries in hospital in Kabul, he added.
President Nicolas Sarkozy offered his condolences to the serviceman's family while reaffirming French support for Afghans as the transition process continued, a statement said.
Prime Minister Francois Fillon paid tribute to the "dedication and professionalism" of soldiers engaged in providing security in Afghanistan and aiding its reconstruction.
The circumstances were virtually identical to the incident in which the last soldier killed there died, in the same region on June 18.
Florian Morillon, 20, also belonged to the Pamiers regiment.
Sarkozy announced on Friday that "several hundred" of the 4,000 French troops in Afghanistan would be withdrawn before the end of 2011.
The president said he shared US President Barack Obama's belief that security had improved since the death of al-Qaeda leader Osama bin Laden and that the handover to Afghan troops and police was taking place smoothly.