Nature got into the way of Breen's plans to be a jockey when he grew almost 6 inches the winter he turned 16. Breen went to work as an exercise rider and was an assistant to trainer Walter Reese by the time he was 18.
The New Jersey native operated a small stable from 1992 to 1994 then worked as an assistant to Ben Perkins Sr. until Perkins retired in 2000. He went out on his own again and became the private trainer for George and Lori Hall at the end of the 2006 season at his home base of Monmouth Park. Breen has been a successful trainer through the years, but, led by Belmont Stakes winner Ruler on Ice, he reached new heights and earned national attention in 2011. Pants on Fire won the Grade 2 Louisiana Derby and was the second betting choice in the Kentucky Derby. The colt finished ninth. Late in the year he won the Grade 3 Pegasus. Ruler on Ice gave Breen and the Halls their first Triple Crown race winner in the Belmont and went on to finish third in the Haskell Invitational, fourth in the Travers, second in the Pennsylvania Derby and third in the Breeders' Cup Classic.
Breen didn't have a horse in the Kentucky Derby in 2012 with My Adonis scratching from the race as the first ever also eligible but in 2013, he returns with Spiral Stakes winner Black Oynx.