Andrew Kelly, of the British Army’s crack Parachute Regiment, died in a shooting accident at an army base in southern Iraq on 6 May, only weeks after his 18th birthday.
His father Robert Kelly wrote to Blair in the most personal criticism yet of his decision to take Britain to war.
He said in his letter to Blair that he was struggling to come to terms with his son's death, which the Defence Ministry said was caused by a weapon accidentally being fired.
"I cannot begin to explain to you how I feel about the loss of my son, nor do I believe that you care or would understand," Kelly's letter reads.
"Your decision to go to war put my son in the firing line unnecessarily. I hold you personally responsible for my son's death as well as the other servicemen killed."
Robert Kelly served with the Royal Navy for 24 years and is a veteran of the 1982 Falklands conflict when Britain reclaimed the South Atlantic islands from Argentina.
"My son died because the wrong decision was made," Kelly, said.
Blair meeting with British troops
at Umm Qasr on 29 May
"If we hadn't declared war, my son would be alive today. I am not a pacifist and if my son had died fighting a war because someone threatened our country I would still feel proud of him and my prime minister."
Blair is facing a barrage of accusations that he hyped intelligence about weapons of mass destruction to take the country to war.
Recent polls aren’t helping Blair’s case either.
An ICM poll for the Daily Mirror newspaper on Monday showed 66 percent of those questioned believed Blair had misled them – either knowingly or unknowingly – before he sent troops into action in Iraq.