The 26-year-old has made 70 appearances for the U's since his debut in 2007.
Manager Joe Dunne told the club website: "I'm really pleased we've got Mark signed up, I've known him a long time and he is an honest, hard working and talented keeper.
"It's vital we have players like that around because their work ethic rubs off on others."
Cousins, who was offered the new deal at the end of last season, added: "It has taken a bit of time to assess things but I'm pleased that I've signed and I'm really looking forward to being back in with the lads and to the new season."
- Sports & Recreation