The 27-year-old Scotland international, who was the subject of three rejected bids from Middlesbrough during the summer, put pen to paper on a fresh four-year deal at Elland Road yesterday.
"I'm delighted to sign a new contract with the club," McCormack told United's official website.
"I've said all along that this club is where I want to be and where I want to play my football. My family are settled here, I love the place, and I'm looking forward to the future now.
"I'd like to thank the manager and the owners for showing faith in me, and I'd like to say a big thank-you to the fans because their support really is something special, and they are what this club is all about."
McCormack scored eight goals in 38 first-team appearances for Leeds last season. He has already found the net four times in six games this term.