Henin closed out the victory with a forehand volley winner, then flipped her racket, buried her head in her hands, leaned on the net and exhaled. She became the first woman since Monica Seles in 1990-92 to win three consecutive Roland Garros titles, and only the second since 1937.
Ivanovic, a Serb playing in her first Grand Slam final, started well before her play deteriorated. The first sign of trouble came when she awkwardly hit a serve 10 feet long, prompting groans from the crowd. She double-faulted to fall behind 3-1, and the unforced errors came in flurries after that.
Henin trailed in each of the first four games, which took 24 minutes, but won 18 of the next 22 points.
Pumping her fist after nearly every point she won, Henin kept up the pressure in the second set with a vast repertoire that ranged from delicate backhands to overhead smashes. During the final changeover she pulled a note out of an envelope bearing the word "Allez" — French for "Let's go."
Then she finished the job. Ivanovic shanked consecutive shots during one rally to fall behind 30-0, and Henin closed out the victory two points later.
On Sunday, top-ranked Roger Federer will bid for the only Grand Slam championship to elude him when he plays Rafael Nadal, who will try to become the first man since Bjorn Borg in 1978-81 to win three consecutive French Open titles.
Federer is seeking his fourth consecutive major title, something last accomplished by Rod Laver in 1969.
Henin extended an Open era record winning streak of 35 consecutive sets at Roland Garros. She became the first top-seeded woman to win the title since Steffi Graf in 1996.
The Belgian became the fifth woman since 1925 to win the French four times. Chris Evert leads with seven titles.
Henin won the French Open for the first time in 2003 and now has six Grand Slam titles, moving her ahead of Venus Williams and Martina Hingis. She trails only Serena Williams' eight among active women.
Henin won $1.34 million — same as for the men's champion. Ivanovic, the first player to represent Serbia in a major final, received $670,000.