Rumours that the pair were to marry were fuelled after Jolie was spotted wearing what appeared to be an engagement ring during a private viewing at Los Angeles County Museum of Art's Chinese Galleries on Wednesday (April 11).
Pitt's representative Cynthia Pett-Dante has since told Reuters: "Yes, it's confirmed. It is a promise for the future and their kids are very happy. There's no date set at this time,"
The design of the engagement ring was a collaborative effort between Brad Pitt and jeweler Robert Procop, reports The Hollywood Reporter.
"I can confirm that, yes, Robert Procop did indeed design an engagement ring for Angelina Jolie, designed in collaboration with Brad Pitt," a Procop representative said.
"Brad had a specific vision for this ring, which he realised over a yearlong collaboration," the rep added. "He wanted every aspect of it to be perfect, so I was able to locate a diamond of the finest quality and cut it to an exact custom size and shape to suite Angelina's hand.
"Brad was always heavily involved, overseeing every aspect of the creative design evolution. The side diamonds are specially cut to encircle her finger. Each diamond is of the highest gem quality."
Procop and Jolie have previously worked together, designing 'The Style of Jolie' collection to raise funding for a school in Afghanistan. Jolie also has worn Procop pieces on the red carpet and her movie The Tourist.
Earlier this year, Pitt said that he won't wed Jolie until there's marriage equality. The couple have six children together.
Watch the trailer for The Tourist below: