The top-ranked player in women's tennis won her 34th career title and fifth this season.
Mauresmo held a 3-1 lead after a first set service break, but Henin pulled even in the seventh game on her sixth break point.
"It's another title for me and gives confidence," said the top-seeded Henin after her 30th match victory of the season.
"Amelie is one of the best players on grass and she proved it last year at Wimbledon. I'm a little bit tired because of the wind, not because of the tough match."
Mauresmo, the second seed and the No. 4 player in the latest rankings, fell to 6-8 lifetime against Henin. One of those six wins came at last year's Wimbledon final.
"Not enough first serves in," Mauresmo said.