Butters escaped while being walked around Magor services by her owners, who were going on holiday.
She was eventually rescued from a bush by Gwent Cats Protection, who then used Butters' microchip to track down her owners, who picked her up the next day and took her back to London.
Glynis Davies from Cats Protection Gwent said: "This story shows the importance of microchipping in being able to reunite lost pets with their owners."
Once they had found Butters' microchip, Ms Davies' fellow rescuer Tina Harty was able to look up the owner's details on a database, including finding their phone number and email address.
Cats Protection was first alerted by rumours online of the cat at the service station.
The friendly feline had been "going up to a lot of people" looking for food before she was rescued, according to Ms Davies.
In fact, she was "so friendly [workers at the hotel at Magor services] were worried someone was going to pick her up" and take her home for themselves.
Instead, Butters' owners were "thrilled to bits" to have her back as they "didn't expect to see her again", according to Ms Davies.