The 22-year-old had already become the highest-ranked Romanian in the history of women's tennis earlier this year, but is now assured of a climb to third after reaching her first grand slam final with a 6-2 7-6 (7-4) victory.
After setting out her stall with two breaks of serve to claim the opening set, Halep was made to fight for the win in the second as a resolute Petkovic forced the tie-break.
But the fourth seed saw out the match to book her place alongside Maria Sharapova in Saturday's final.
Prior to this year's tournament, both Halep and Petkovic had failed to progress beyond the last eight of a major, nor registered a set in a quarter-final encounter.
However, the pair comfortably came through their encounters against Svetlana Kuznetsova and Sara Errani respectively to set up a last-four clash.
And Halep was on the front foot from the off, instantly breaking her opponent's serve to take control.
Another dropped service game for Petkovic saw her fall a set behind, but she showed greater resolve in the second as she desperately tried to cling on to her place in the tournament.
The German went 3-1 up after breaking Halep's serve, before that advantage was immediately cancelled out.
The two players were evenly matched for the remainder of the set, but when only one of the opening eight points in the tie-break went with serve, it looked as though the first player to claim points on back-to-back deliveries would emerge victorious.
And that proved to be the case, as Halep finally put the encounter to bed and avoided a deciding set.
Saturday's final will see Halep and Sharapova renew acquaintances after the former lost this year's Madrid Open final to the Russian having initially won the opening set 6-1.