"It's hard to think about it and find the right words," Armstrong said after receiving the winner's yellow jersey from Paris Mayor Bertrand Delanoe.
"This was definitely my most difficult race out of the five ... I have always loved cycling and I made it my job. And next year I will be back to try to win a sixth title."
Only Spain's Miguel Indurain Spain had previously secured five straight victories (1991-95).
On the final 94.5-mile stretch between Ville d'Avray and Paris, Armstrong took no chances, biking well back in the pack. He won the tour in 83:41:12 -- just over a minute ahead of German rival Jan Ullrich, who dashed his own chances when he crashed into a hay bale Saturday.
Australian Baden Cooke won the green points jersey as the best sprinter. Jean-Patrick Narzon of France won the last stage to the Champs Elysees in Paris in 3:38.49.