The engaged couple, who have had to spend time apart due to conflicting work schedules, looked absolutely smitten to be reunited, onlookers said.
While Jennifer, 45, and Justin, 42, didn't hit the dancefloor at the swanky CAA-hosted party, "they stuck together and were holding hands," an insider told E! News.
"They seemed happy!" the source added. The loved-up couple were seen happily chatting with Julia Roberts, Jessica Biel, John Mayer, Charlize Theron and Sean Penn among other A-listers.
Justin Theroux and Jennifer Aniston at a party in 2012
Jennifer and Justin will have no doubt wanted to make the most of their time together and revel in the pre-Oscar excitement.
The following evening, the Hollywood star couple were seen heading out to another bash where they spoke of their low-key plans for the film awards ceremony – to "stay home and watch in their pyjamas."
While neither of them were nominated and therefore did not receive an invitation to the prestigious Oscars affair, it seemed Jennifer and Justin preferred not to attend any of the high-profile viewing afterparties either.
Justin and Jennifer at the Oscars last year
In recent months the pair, who have been engaged since 2012, have faced a barrage of rumours that their relationship was on the rocks.
Jennifer spent her 45th birthday apart from her fiancé and celebrated with an intimate dinner in Los Angeles with best friend Courteney Cox and other pals. Justin, meanwhile, was on the opposite side of the country in New York, filming for his new HBO show The Leftovers.
Just last month reports emerged that they had put their wedding plans on hold.
"There is absolutely no wedding talk or planning going on," a source close to the couple told RadarOnline. "Publicly the couple is saying it's because they are just too busy with work, but if they wanted to get married, it would happen."
"The relationship is definitely at an impasse," added the source. "Either it's going to fizzle out, which seems likely, or they get married."