He played college football for the Florida State Seminoles, earning consensus All-American honors in 2014.

[1][2] He attended Dwyer High School in Palm Beach Gardens, Florida, where he played football and lacrosse.

[5] After considering entering the 2014 NFL draft, O'Leary returned to Florida State for his senior season.

[6] During his senior season, he set Florida State's record for career receptions for a tight end.

[13] On November 12, 2017, in a 47–10 loss to the New Orleans Saints, he caught his first career touchdown, a seven-yard pass from quarterback Nathan Peterman.

[17] He scored his first touchdown with the Dolphins in Week 6 against the Bears on a five-yard pass from Brock Osweiler.

[23] In 2023, O'Leary joined Florida State as a student assistant coach, working with the offense.