The Belgian wild card, warming up for her first appearance at Roland Garros since winning her fourth French Open title there in 2007, won 6-3, 6-2 and will meet Samantha Stosur in Sunday's final.
The Australian, seeded seven, beat Russian qualifier Anna Lapushchenkova 7-5, 6-3.
Henin has already reached the finals at Brisbane and the Australian Open since returning to action in January following a 19-month break from the game.
Peer hit back from an early service break to level at 2-2 but after that had little answer to the ruthless Henin, whose only problem was with her first serve.
"It has been a great performance," Henin told reporters.
"I feel really comfortable at the moment and am enjoying being on the court, especially at one of my favourite tournaments.
"My coach will nevertheless tell me first about the mistakes I made. But he'll also say that I was good enough today. And that I'm better when I'm playing aggressively and going to the net.
"My quarter-final was long and intense. I was a little tired especially as I didn't sleep that well. But physically, I was fine," she added.
World number 10 Stosur continued her unbeaten record on clay this year against the rank outsider.
"I had a little bit of trouble at the start," she said.
"There were hardly any rallies and I couldn't really get into the match. Anna made me work hard and I had difficulties working out how to play her. It wasn't easy today," she added.
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