The 19-year-old has signed a contract that will keep him at the KC Stadium until 2014.
Stewart arrived on loan in November via a two-month spell at Yeovil and has made 11 appearances for Nigel Pearson's side this season.
Pearson said: "We're absolutely delighted to have secured Cameron's services on a permanent deal.
"He's a player who has shown plenty of promise during his time here so far and he's a very bright future in the game."
Source: PA
Source: PA