Kelly selected Clemson over Alabama, Florida State, Purdue, Syracuse, Buffalo and Michigan State.
Ranked as the No. 29 quarterback in the class of 2012, he arrived to Clemson for an unofficial visit on Tuesday night and stayed until Wednesday evening. Kelly spent the night at Alabama before his trip to Clemson.
His announcement was made St. Joseph Collegiate Institute [Buffalo, N.Y.] around 3 p.m. It became an official commitment at 3:15 p.m. when the Clemson coaches were notified.
Chad Morris served as the primary recruiter for three-star commitment Chad Kelly.
With Kelly's pledge, Morris has picked up his first commitment since joining the Tigers' staff in January.
Clemson was recently designated as the favorite over the Alabama and Florida State.
"After just talking to coaches and other people, it pretty much sealed the deal… it just seems like it would be a good fit and everything," Kelly told CUTigers.com on May 27.
This week's overnight visit was his second trip to Clemson. Before he left on Wednesday, he was projected to make a commitment to the Tigers.
Kelly threw for 2,159 yards with 25 touchdowns and ran for 1,057 yards with 14 scores as a junior at St. Joseph's Collegiate Institute.
The Thursday announcement makes it the Tigers' fifth commitment in eight days, increasing the 2012 class to nine.
Kelly's uncle is Hall of Fame quarterback Jim Kelly.
CUTigers.com will have an interview with Kelly later today.