The 24-year-old recovered from ligament damage and a fractured fibula on the opening day before featuring 11 times as Gareth Ainsworth's men finished the season strongly.
"I'm very pleased to be staying as Wycombe are a club close to my heart," the Antigua & Barbuda international told the club's official website.
"I'm glad to get it sorted and I've been working hard all summer so that I'm ready to get back and play.
"From when I got offered the contract, I knew I wanted to stay and this is the club I wanted to play for next season.
"There were just a few things that needed to be sorted, but they are now and I'm pleased that it's done."
McCoy follows Matt Bloomfield, Dean Morgan, Jesse Kewley-Graham, Lee Angol and Max Kretzschmar in agreeing new deals this summer.