The serviceman, from 1st Battalion Grenadier Guards, was injured as a result of enemy action in the Nahr-e Saraj district of Helmand Province on August 14.
He died from his injuries at Queen Elizabeth Hospital in Birmingham yesterday, the MoD said.
Task Force Helmand spokesman Major Ian Lawrence said: "It is my duty to inform that, very sadly, a soldier from 1st Battalion Grenadier Guards has died as a result of wounds sustained while on duty in the Nahr-e Saraj district of Helmand Province. The thoughts and prayers of everyone serving in Task Force Helmand are extended to his family and friends at this extremely difficult time."
The soldier's death brings the number of members of UK forces to have died since operations in Afghanistan began in October 2001 to 426.