The actor's face will be superimposed onto the body of a baby for new movie The Curious Case of Benjamin Button, which is about a man who is born 70-years-old and ages in reverse.
Director David Fincher toldBritain's The Times newspaper: "In the past you may have had different actors playing him at different stages of his life, but here I can use Brad Pitt throughout, just putting his head on different people's bodies.
"I really think that it will work. At least I hope it does, if not, it's going to look bloody awful!"
But the filmmaker is confident movie goers will be convinced by the computer wizardry used to make Brad a baby.
Fincher added: "I don't think an audience is going to be able to tell the difference between a film shot digitally or on film. "Technology moves on, and it's going to be vital for the film."
The movie, based on the short story by F. Scott Fitzgerald, also stars Cate Blanchett, Tilda Swinton and Brad's daughter Shiloh.
Shiloh - who turns one on May 27 and is Brad's child with partner Angelina Jolie – has a cameo role playing Cate as a baby in the movie.
A source recently revealed: "Brad and Shiloh saved the day when twin sisters hired to take turns playing Cate Blanchett's character as a baby wouldn't settle down.
"Everyone waited in vain while the babies were fed, changed and hugged - but nothing worked to calm them on the set in New Orleans.
"Then quick-thinking Brad realised his daughter's happy and mellow disposition made her a quick fix for the role."
Shiloh, who had been playing at the on set day care centre, was swiftly put in costume.
The source added: "She's a natural. Shiloh did her scenes perfectly and was giggling and happy throughout her big day."
