The 18-year-old American forward led Canadian Hockey League juniors with 145 points (62-83) in 58 games last season with the Ontario Hockey League's London Knights.
"Patrick is a dynamic and exciting young player," Hawks GM Dale Tallon said in a statement. "We're pleased that he will begin a long and productive career with the Blackhawks when we open camp on Sept. 13.
"Patrick will get every opportunity to earn a spot on the opening night roster."
The native of Buffalo, N.Y., was OHL rookie of the year in 2006-07 as well as a first-team all-star. He also had nine points (5-4) in nine games as the United States took home bronze at the world junior hockey championship last winter.