The Belgian player beat the second-seeded Frenchwoman in 1 hour, 42 minutes to add to her titles of 2003, 2004 and 2006.
It was Mauresmo's second consecutive final, after she won in Antwerp, Belgium, last week.
The second-ranked Henin was playing in her second tournament of the year. It was Henin's 30th title on the WTA Tour and her seventh win against third-ranked Mauresmo out of 13 matches.
"It's just amazing. I am so delighted," said Henin. "I think I played a very good match today, against a very good player ... To win against someone like Amelie, and to win a title in only my second tournament back, it is just great."
Henin took control with 21 forehand winners, against 10 for Mauresmo, who was let down by weak second serves. Mauresmo won 31 percent of the points on her second serve, compared to 54 percent for Henin.
Henin raced to a 4-1 lead in the first set before Mauresmo settled down and pulled back to 4-4. But Henin broke her again in the 10th game to win 6-4.
It was much closer in the second set, and Mauresmo had a chance to go 2-0 up but Henin saved the break point with a brilliant backhand winner.
With the game deadlocked at 5-5, Henin rattled off one winner after another, dominating the net as she broke Mauresmo at love to go up 6-5.
Henin closed the final match with a drop shot and then a powerful forehand.
"Justine deserved to win. She played very well out there," Mauresmo said.
In the doubles' final, top-seeded Cara Black of Zimbabwe and Liezel Huber of South Africa beat wildcards Svetlana Kuznetsova of Russia and Alicia Molik of Australia 7-6 (6), 6-4.