The former NSW State of Origin representative extended his stay at the Knights after scoring a double in Monday's round one thrashing of the Wests Tigers.
The 27-year-old debuted for the club back in 2007 and has played 110 games, scoring 46 tries.
McManus forms a lethal back-three combination at the Knights alongside Darius Boyd and Akuila Uate.
"We are pleased to re-sign James," said Knights chief executive Matt Gidley.
"He is the ultimate professional and sets a high standard at our club.
"James is a player who is highly respected for the professionalism he displays on and off the field.
"We think James has his best football ahead of him and his consistency has been rewarded with an opportunity to continue to represent our club."