"Justin Theroux had an amazing birthday on Friday, receiving an extraordinary gift when his girlfriend, Jennifer Aniston, accepted his proposal of marriage," Theroux's representative told People magazine.
According to the magazine, the couple, who both starred in the movie Wanderlust, started dating in May 2011.
Aniston, 43, married Hollywood star Pitt in 2000, but the marriage ended in divorce in 2005 following reports that Pitt had been unfaithful to Aniston with his another Hollywood mega-star, Angelina Jolie.
Theroux, 41, has not been previously married.
Aniston rose to Hollywood stardom while playing Rachel Green in the situation comedy Friends that ran on the NBC network for 10 years starting in 1994.
In that role, she earned several major awards, including an Emmy and a Golden Globe Award.
She starred in a series of successful movies like She's the One, The Good Girl, Bruce Almighty and The Break-Up.
Last February, she received her own star on the Hollywood Walk of Fame, a sign of industry recognition of her talent and achievement.
Her post-Brad Pitt relationships included actor Vince Vaughn, with whom she co-starred in The Break-Up.
But it ended in a split in 2006 as did her subsequent confirmed and reported liaisons with British model Paul Sculfor and pop singer John Mayer.
Watch Video: In this Video Justin Theroux talks Jennifer Aniston
Theroux's career path is much more modest. He is best known for his work in the films Mulholland Drive and Inland Empire.
He played John Hancock in the 2008 HBO TV mini-series John Adams. He directed his first film Dedication in 2006, which made its debut in 2007 at the Sundance Film Festival, a venue for budding American filmmakers.
But he has a stellar pedigree, being related to novelists Paul Theroux, Alexander Theroux and author Peter Theroux.
The engagement was largely expected as the couple was reported to have purchased a mansion in Los Angeles's exclusive Bel-Air neighborhood for roughly $22 million.
Watch The trailer of Justin-Jennifer's Wanderlust
