Theroux celebrated his 41st birthday on Friday and his reps confirmed to PEOPLE that the writer and actor popped the question.
"Justin Theroux had an amazing birthday on Friday, receiving an extraordinary gift when his girlfriend, Jennifer Aniston, accepted his proposal of marriage," his rep told the magazine.
Aniston, the reigning 'Sexiest Woman of All Time' has been dating Theroux for a little more than a year.
NY Daily News reports that Theroux and Aniston first met about five years ago on the set of “Tropic Thunder”, a film written by Theroux.
Rumors of a relationship started to swirl in May 2011 after they co-starred in the film Wanderlust. "They are great friends," a source told PEOPLE at the time after the two were spotted dining together at Los Angeles's Sunset Tower Hotel.
The couple have become tabloid favorites for dressing alike, often in their favorite accessory - black leather.
This is the second marriage for Aniston who married actor Brad Pitt in July 2000. The marriage famously broke down and Pitt started dating his Mr. & Mrs. Smith co-star, Angelina Jolie.
Pitt and Jolie, who have six children together, announced their engagement five months ago and were the subject of intense wedding speculation this weekend. Their Chateau Miraval home in the south of France was setting up for an anniversary party for Pitt's parents but tabloids speculated the party was a cover for a covert wedding ceremony.