The 25-year-old, who had one year remaining on his previous deal, has put pen to paper on a contract that will cement him to the club until 2014.
"I know this was where I want to be," Foden said. "I've seen the club climb and achieve bigger things with every season. I was pretty quick in putting pen to paper and signing for two more years.
"We achieved some great things last year and reached a major final, although we came up just short. But I'm excited to be here and I'm looking forward to a long future here."
The England full-back, who has racked up 20 tries for the Saints, joined the club from Sale Sharks three years ago.