The 22-year-old from Bristol was shot during an insurgent attack in Nahr-e Saraj, Helmand Province, on 14 August. He later died in Queen Elizabeth Hospital, Birmingham, on Friday. The father of one joined the Army in 2009 and deployed to Afghanistan for the first time on April 5 this year.
His family said: "Karl was one in a million. He was a proud and caring man who took pride in whatever he did. The family are obviously devastated. Karl was the light of many lives and touched all who knew him. He will be especially missed by his baby daughter Grace, who has lost her number one man."
Lieutenant Colonel James Bowder, Commanding Officer of 1st Battalion Grenadier Guards, described Guardsman Whittle as "one of our very best. A great soldier and a young man of rare character, he was destined to go a very long way in the Army."
He added: "I am immensely proud of what Guardsman Whittle achieved out here in Afghanistan and more broadly during his military career. He was utterly committed to his fellow guardsmen, his company and the mission. He will never be forgotten by either the battalion or the broader regimental family."
After completing his combat training, Guardsman Whittle spent time conducting public duties at the Royal Palaces and taking part in state ceremonial tasks with Nijmegen Company, Grenadier Guards. In August 2011, he joined 1st Battalion Grenadier Guards as part of Three Platoon, The Queen's Company, and later deployed to Afghanistan.
A statement from the Ministry of Defence said: "Guardsman Whittle was one of the leading lights of his Company. He was compassionate, selfless and, despite his comparative inexperience, a figure others would turn to in the face of adversity."
His death brings the number of UK military deaths in the Afghanistan operation, since 2001, to 426.