The soldier died as a result of an explosion that happened near Sangin, in central Helmand province, during the afternoon of Friday 22 January 2010.
Spokesman for Task Force Helmand, Lieutenant Colonel David Wakefield, said:
"It is my sad duty to inform you that a British soldier from A Company, 4 RIFLES, serving as part of 3 RIFLES Battle Group, was killed by an explosion near Sangin in Helmand province earlier today.
"He was on a foot patrol, part of a larger operation to provide security for the local population in Sangin, when the explosion happened.
"His courage and the sacrifice he has made will not be forgotten."
The soldier's next of kin have been informed and have asked for a period of grace before further details are released.