Rules prohibit players from signing while still in school. The deal was finalized and announced on Friday after Mesoraco passed his physical.
Taken 15th overall in the 2007 First Year Player Draft on June 7, Mesoraco starred behind the plate for Pennsylvania's Punxsutawney High School. He will immediately report to the Reds' Gulf Coast League affiliate in Sarasota, Fla.
The contract is a Minor League deal with terms of Mesoraco's likely seven-figure bonus not revealed by the Reds.
Mesoraco, who turned 19 on Tuesday, had a scholarship waiting at the University of Virginia to fall back on as potential leverage for a better deal but said on Draft day he wanted to join the Reds. He should benefit from signing quickly rather than sitting out as negotiations dragged on through the summer.
"That helps a lot," Buckley said by phone from Florida. "That first year for anyone, even college players, is a transitional year. There are wooden bats. Instead of playing three times a week, you're playing five or six times a week. He'll go from Pennsylvania to the humidity of Florida and play every day.
"It's good to get that first year behind you."
A 6-foot-1, 195 pounder that bats right-handed, Mesoraco participated in the Pennsylvania high school state tournament. He finished his high school career batting .467 with four homers, 21 RBIs, a .632 on-base percentage and a .911 slugging percentage. He was named his state's Gatorade Player of the Year.
"He did very well and had a terrific season, as did his team," Buckley said. "We're happy to have him."
Mesoraco was the first catcher taken in the first round by Cincinnati since Dan Wilson in 1990.
The Reds made 50 picks in the Draft and have signed close to 30 of them. New rules set an Aug. 15 deadline to sign selected players or the team's rights would be lost. That effectively ended the practice of "draft and following" players.
"We're almost finished," Buckley said.