In the 1984 Golden Gloves he fought out the Times Square Boxing Gym again lost a split decision in the heavyweight division to Ira Turner, the eventual champion.
Seamus declined, returned to Brooklyn and in 1985 won the New York State Golden Gloves heavyweight division scoring KO's in all four of his victories.
Later that year he turned professional and used the money he obtained from the signing bonus to pay for his second semester at Saint John's University.
Later that year he won "Rusty Staub's" famous rib eating competition representing Madison Square Garden.
In the spring of 1990 the world of boxing was shocked when the seemingly unbeatable Iron Mike Tyson was KO'd by challenger Buster Douglas.
On 1 June 1990, McDonagh took Tyson's place and fought WBC Continental Americas Heavyweight Champion Evander Holyfield [1] He lost by a TKO in the fourth round.