The pair announced their plans to split by releasing a joint statement via a spokesperson.
'In an effort to reduce any further speculation, we have decided to announce our separation. This decision was mutual and lovingly made at the end of last year,' it began.
'We are two best friends who have decided to part ways as a couple, but look forward to continuing our cherished friendship. Normally we would do this privately, but given that the gossip industry cannot resist an opportunity to speculate and invent, we wanted to convey the truth directly.'
Jennifer and Justin went on to say that despite the fact they will no longer be an item, they hope to remain on good terms.
They continued: 'Whatever else is printed about us that is not directly from us, is someone else's fictional narrative. Above all, we are determined to maintain the deep respect and love that we have for one another.'
Jennifer and Justin, 46 - who were last pictured together while enjoying a break in Mexico at the start of 2018 - first met in 2007 when they starred alongside one another in the movie Tropic Thunder.
In 2010 they were re-united as co-stars while shooting the film Wanderlust. It's then that their romance is thought to have blossomed. Justin popped they question two years later on 10 August 2012.
'Justin Theroux had an amazing birthday Friday, receiving an extraordinary gift when his girlfriend, Jennifer Aniston, accepted his proposal of marriage, his rep said at the time.
The actress and Justin exchanged vows in the summer of 2015 when they threw a surprise wedding at their LA home on 5 August.
Before tying the knot with Justin, the 49-year-old Friends star was married to Brad Pitt.