Cornelius was born in Thomasville, Alabama to Ted, a school principal, and Ila Cornelius, a teacher's aide. His older brother, Pat, played college baseball at Auburn. He maintained a 97.6 grade average at Thomasville High School. He planned to play college baseball at Mississippi State but chose instead to begin a professional career after being taken in the eleventh round of the 1988 Major League Baseball draft by the Montreal Expos and receiving a signing bonus of $225,000 (equivalent to $598,000 in 2024).[1] According to his father, it was the largest contract ever given to a high school draftee.[2] He began his professional career with the Rockford Expos of the Midwest League.[3]
Cornelius was the Miami Marlins' bullpen coach from 2010 to 2016. He was named the pitching coach for the Atlanta Braves' Triple–A affiliate, the Gwinnett Braves, prior to the 2017 season.[4]
Cornelius was named as the pitching coach for the Jupiter Hammerheads of the Miami Marlins organization for the 2019 season.
Cornelius was named the bullpen coach for the Colorado Rockies on December 13, 2021.[5] On October 8, 2024, Cornelius and the Rockies parted ways.[6]
In 2025, Cornelius was named pitching coach for the Louisville Bats the Triple-A affiliate of the Cincinnati Reds.
