The Romanian's 6-4, 3-6, 6-3 victory sets a final clash with 20-year-old Jelena Ostapenko and leaves Halep one victory from her first Grand Slam final and the WTA's No.1 ranking as well.
Jelena Ostapenko celebrated the flawless birthday present with a spot in her first grand slam final.
Should Ostapenko, who had never won a match at the French Open before last week, beat Halep she would become only the second unseeded player to win the women's title after Great Britain's Margaret Scriven achieved the feat in 1933.
"I really happy, I love to play here and I'm just happy the way I celebrate my birthday", Ostapenko grinned.
"When I came here, of course I didn't expect I would be in the final", Ostapenko said.
"In the third set I just wanted to stay playing aggressive".
A rasping Pliskova forehand gave her a battling hold and she warmed to the task in the second set, causing Halep far more problems with brutal groundstrokes and a venomous serve as she broke for the first time to take a 4-2 lead.
The French Open champion will be a first-time major victor while victory will also crown the Romanian third seed as the new world number one, replacing Angelique Kerber.
For 30th-seeded Bacsinszky it was a second semi-final defeat in three years in Paris. Once she started to pick up steam, it was clear that playing uphill had taken its toll on Pliskova, and Halep took her final two games with relative ease. I hope I can play better and win it.
The third seed was briefly dumped by coach Darren Cahill in March due to her poor attitude and the Australian will certainly know he made the right decision in coming back after this superb display of fighting spirit. "That gap won't be there at Wimbledon because (Maria) Sharapova will come back, Victoria (Azarenka) will come back, (Petra) Kvitova will be better than ever", Evert said.
Saturday's final will see a new Grand Slam champion crowned, and a new name at the top of the rankings should Halep win and overtake Angelique Kerber.
The Romanian was under pressure early in the decider but finally chased down a forehand and fired a brilliant cross-court victor to grab a 3-1 lead.
"But then, like, first match was a tough match, as well, and I won it". She has proven time and time again that she is very much an "in the moment" tennis player.
Ostapenko crunched 50 winners to Bacsinszky's 22 but her raw attacking instinct also brought 45 unforced errors to the Swiss counter-puncher's 19.
She produced a string of stunning winners to take a thrilling first set 7-6.
Halep beat second seed Karolina Pliskova 6-4, 3-6, 6-3 to reach the French Open final for the second time. Halep looks for her first career grand slam title, and this is her second grand slam final appearance.