2009-10: Troy Donnay played for the Belle Tire midget major team in Michigan. He scored 3 goals with 18 assists and had 91 penalty minutes in 65 games. He was selected by London in the fourth round (79th overall) of the 2010 OHL Priority Draft.
2010-11: Donnay appeared in 25 games in his first season with the London Knights. He had 1 assist and was -2 with 12 penalty minutes. London reached the playoffs after finishing fifth in the Midwest Division. The Knights took eventual OHL champion Owen Sound to six games in a first round playoff series but Donnay did not see any action.
2011-12: Donnay played 27 games for London in his second OHL season — scoring his first goal while playing forward — before being obtained by Erie in a January trade. In 50 games between the two teams Donnay scored 1 goal with 7 assists and was -24 with 44 penalty minutes. The Otters missed the playoffs; finishing with the OHL’s worst record. Donnay was ranked 122nd amongst North American skaters in Central Scouting’s final rankings but was not selected in the 2012 NHL Draft.
2012-13: Donnay was an assistant captain and logged major minutes for Erie in his third OHL season. He scored 1 goal with 7 assists and was -39 with 48 penalty minutes in 68 games. The Otters showed improvement, finishing 21 points better than in 2011-12, but once again missed the playoffs after finishing fifth in the Midwest Division. Donnay signed a three-year entry-level contract with the Rangers in July of 2013.
2013-14: Donnay returned to Erie for his third OHL season and played for the USA U20 team at the 2014 World Junior Championship. He scored 2 goals with 17 assists and was +40 with 92 penalty minutes in 66 regular season games for the Otters. Erie finished second in the Midwest Division behind Guelph and reached the Eastern Conference finals before falling to the Memorial Cup champion Storm. Donnay scored 1 goal with 1 assist and was -1 with 12 penalty minutes in 14 playoff games. He had 3 assists and was +2 with 2 penalty minutes in five games for the USA at the 2014 WJC. The USA finished fifth, falling 5-3 to Russia in the quarterfinals.
2014-15: Donnay skated for the Rangers’ prospect team in the Traverse City tournament and attended training camp before being sent back to Erie for an overage season. He played 45 regular season games for the Otters, missing time early in the year due to injury and receiving a 10-game suspension at the end of February. Donnay scored 4 goals with 19 assists and was +26 with 53 penalty minutes. Erie finished first in the West Division and reached the OHL finals — falling in the playoffs to the eventual Memorial Cup champion Oshawa. Donnay had 5 assists and was -3 with 21 penalty minutes in 19 playoff games.
Donnay will begin his pro career in 2015-16 following an overage season with the OHL's Erie Otters. He will challenge for a spot with the Rangers' AHL affiliate Hartford but could begin the year in the ECHL.