The pair met up with the documentary filmmaker for dinner at Shoreditch House following a screening of Horrible Bosses on Wednesday, an eyewitness told Us Weekly.
The trio spent several hours dining and sharing drinks, with the insider claiming that Louis "obviously approved" of Aniston.
The source added: "It looked like they were having a great time, and they all seemed instantly at ease with each other. Justin looked proud of Jen and seemed quite manly and protective."
Justin Theroux, who apparently began dating Aniston earlier this year, recently joined her at a Hollywood ceremony to honour her career achievements.
Aniston has remained tight-lipped about her romance with Justin, but recently admitted in a Good Morning America interview that she is "very happy" with her private life.
Horrible Bosses is now playing in the US and opens in the UK on July 22.
> Jason Sudeikis: 'Jennifer Aniston is obscene in Horrible Bosses'
> Jennifer Aniston: 'Friends might be my greatest job'
Watch Jason Bateman, Jason Sudeikis and Charlie Day talk to Digital Spy about Horrible Bosses below:
Watch the Horrible Bosses trailer below: