The 34-year-old, who joined the O's in 2011, has made 69 appearances for the club, but his initial contract was due to expire at the end of the season.
"Kevin is a huge player for us and to get his commitment moving forwards is massive. He's a class act and an excellent pro who offers us valuable experience and quality both on and off the pitch," Orient boss Russell Slade told the club's official website.
"He's excellent with the younger players and they can learn a lot from him. He attracted some interest in the transfer window so for him to see his future with us gives an indication of what we are building here and it's great for the club."
Orient currently sit 13th in the League One table.