He was named last night as Private John King, 19, of the 1st Battalion, who died in a blast in the Nahr-e Saraj district of Helmand Province on Friday.
The Ministry of Defence said Private King was taking part in a partnered foot patrol with Afghan national security forces to increase security around the village of Llara Kalay.
It said in a statement: “The Afghan National Army members of the patrol came under fire from insurgents and the International Security Assistance Force soldiers moved forwards to support them.
“During the firefight Private King was caught in the blast from an Improvised Explosive Device and was killed in action, despite the best efforts of medics at the scene.”
Private King, from Darlington, joined the Army in 2009 and deployed to Afghanistan in October.
He leaves mother Karen, father Barry, brothers Ian and Stephen and girlfriend Kelly.
His family said: “John was a tremendous son, brother and boyfriend. He was a devoted grandson, a loving family member, and a proud soldier who died doing a job he adored.
“He will be sadly missed by all his family, friends, and loyal German shepherd dog Rex.”
Lieutenant Colonel Dan Bradbury, Commanding Officer, 1st Battalion, said: “Private King had been part of the 1st Battalion The Yorkshire Regiment for a little over 18 months – but one of the busiest 18 months in the Battalion’s recent history.
“From early on he was able to fit in quickly through a combination of hard work, grit, a willingness to endure difficult conditions and an irrepressible sense of humour.
“Always the first to volunteer for anything, he was one of B Company’s characters: someone who could be found at the front at work or play, and was hugely popular as a result. His cheeky smile – no matter what we were doing – is the thing we will miss most of all.”
A total of 394 British troops have died since the start of operations in Afghanistan in 2001.