Having also defeated top-ten player Jo-Wilfried Tsonga in the second round here, Haas again proved last year's persistent shoulder injury is behind him by beating Djokovic who has struggled on the grass on occasions this week.
This was the 31-year-old's first win over Djokovic, the top seed here after French Open champion Roger Federer withdrew on Tuesday.
"It is unbelievable," admitted Haas in front of a delighted crowd. "When I travelled here, I would have never believed that I would end the week with the title. I would like to thank the public for their great support, it has really been a wonderful week for me."
Having come from behind to beat compatriot Philipp Kohlschreiber in the semi-final, former world number two Haas, now ranked 41st in the world, wasted no time to take the first set with ease after just over half an hour.
Djokovic had made hard work of beating qualifier Olivier Rochus from Belgium the day before in his semi-final and his faltering form continued on grass with Wimbledon just a week away.
"Tommy completely deserves the win," admitted Djokovic. "There's a lot of things I should have done better against Tommy. You don't have much chance if you return like that against an aggressive player like him."
The Serb regained some composure in the second set and with both players holding serve, a tie-breaker went Djokovic's way when Haas double-faulted on his own serve.
At the start of the third set, Haas, who lost to Federer over five sets in Paris having squandered a 2-0 lead, broke Djokovic, but the Serb responded in the third game by racing into a 40-0 lead against serve for three break points.
Haas dug deep to hold his serve to take a 3-0 lead, but although Djokovic held his serve to make it 3-1, Haas raced through to win the next three games to claim victory in just over two hours.