The double leg amputee, who took gold and set a world record at the London games, arrived at Land's End in Cornwall last night having left John O'Groats on August 13.
He had earlier described as "exhausting" the challenge in memory of friend Simon Mellows, who died of cancer in 2005, and fellow amputee Terry Fox who died, aged 22, while attempting to run across Canada in 1981. He was raising money for cancer research.
He said: "Despite the constant aches, pains and endless hills there was one thought that kept me going.
"That thought was a determination to prove that anyone and everyone can live a life without limits.
"Once you have accepted this, you can push the barriers as far as they can go.
"I hope I have been able to leave that message with the people across Britain."
Whitehead said he had used a "good few" blades - prosthetic running legs - and had suffered blisters as well as a cold over the past week.
A natural marathon runner, he turned to sprinting because there was no marathon for him to compete in at the London 2012 Paralympics.
This charity challenge is also a million pound fundraising quest as he hopes to raise at least that amount - through donations and sponsorship of people who want to run alongside him - for the charities Sarcoma UK and Scope.