The 17-year-old from Garner, North Carolina, beat fellow teenager Lauren Alaina, who had been been considered the favourite to win the show.
McCreery, a high-school student who also works part-time at a local grocery store, won over audiences with his trademark deep voice.
He is the first country music winner since Carrie Underwood won in 2005.
McCreery is also the fourth consecutive male contestant to win the competition
After being declared the winner, he said: “Never in my wildest dreams. I got to thank the Lord first. He got me here.”
During the finale he sang with country singer Tim McGraw, as well as singing what will become his first single, I Love You This Big.
