The `Twilight Saga` co-stars - who are believed to have been dating since meeting on the set of first movie in the vampire franchise in 2008 - surprised diners with their affectionate display at Soho House restaurant.
An onlooker said: "They were staring at each other throughout dinner and kept stealing quick kisses from one another during the night. Rob`s arm was around her for most of dinner and they kept looking at each other and giggling throughout the evening. They are definitely into each other."
The source added that despite being joined by a large group of friends, the pair didn`t leave each other`s sides all night, while a smitten Robert - who plays vampire Edward Cullen opposite Kristen`s Bella Swan - only had eyes for his girlfriend.
The onlooker added to E! News: "They were by each other`s sides the entire night. After dinner, Rob, Kristen and their friends moved to the patio where the group was smoking and the guys were drinking. Everyone was laughing and having a good time together, but you could tell Rob was doting on Kristen and making sure she was comfortable. They were next to each other everywhere the group went."
The pair will begin filming `The Twilight Saga: Breaking Dawn` - the final part of the vampire series - in November.