The 27-year-old ended the giant-killing run of Nadia Petrova 7-6 (7/3), 7-5 on Rod Laver Arena to become just the third women's wildcard entry to reach the last four of a grand slam.
The previous player to do so was Henin's countrywoman Kim Clijsters in September last year when she memorably returned from retirement, and becoming a mother, to win the US Open.
Henin is on course to replicate that performance less than four weeks after returning from her own 20-month retirement with only unseeded Chinese player Zheng Jie standing between her and the final.
After her win against Petrova, who had eliminated Clijsters and third seed Svetlana Kuznetsova in the previous two rounds, Henin admitted her run at Melbourne Park had exceeded her expectations.
"I remember my discussion with (coach) Carlos (Rodriguez) on the plane when we were flying to Australia we were talking about the goals – it's much more than what we expected," said Henin, who reached the final of her first tournament in Brisbane a fortnight ago.
"I was coming here to see a lot of things. I was curious about what I was going to feel on the court, but now I've won a lot of matches and everything is going well for us.
"I think I have improved a lot in this tournament since in Brisbane.
"I wasn't able to play well in the tough moments at first, but in the last few matches I have been able to. That is probably the most important thing."
Henin admitted she had been inspired by Clijsters' success at Flushing Meadows, but when asked if she was using it as motivation as she closes in on her own dream return, the Belgian said: "Not really. What she did, I did admire that a lot because it's not easy what she did in New York.
"What she did means it is possible for me. But we have very different kind of personalities, different kind of players, so it's always very hard to compare.
"But what she did was just great. That will be a dream for me to do it also."
Henin will now meet world No.35 Zheng in the semi-finals after the 26-year-old swept past Maria Kirilenko 6-1, 6-3 in one hour and 25 minutes.
It is the second time Zheng has reached the last-four of a grand slam after she made it to that stage at Wimbledon two years ago.
"I am so happy to be through," she said. "Before the match I knew it was a big chance to get to a semi-final again so I was nervous early on but I did very well.
"I played aggressive and made a lot of winners."
Zheng revealed her last-four meeting with Henin would have added relevance after admitting the Belgian was her favourite player, but she denied she would be overawed. "It's tough for me, but I'm so happy I can play against her because she is my favourite player," she said.
"I don't have anything to lose, I just want to play my tennis." British teenager Laura Robson progressed to the third round of the girls' championship after beating 11th seed Yulia Putintseva in three sets today.
Robson, who reached the final at the tournament last year, defeated the 15-year-old Russian 6-2, 3-6, 6-2 in one hour and 40 minutes. Robson will now face Romania's Cristina Dinu in the next round tomorrow.