Milligan was a 1981 graduate of Princeton University. He was a defensive back in football, a third baseman in baseball and a wrestler who often wrestled in the highest weight class, despite being only about 5-11, 185 (he would frequently wrestle and defeat 250-pounders, and once wrestled and defeated a 325-pounder in the NCAAs). Milligan earned ten varsity letters, an all-time University record. He was an All American in wrestling and was Princeton's 1981 Senior Scholar-Athlete of the Year, which is the University's highest undergraduate honor. He later earned an M.B.A. degree from New York University.
The New York Mets offered him a minor league contract after his college graduation from Princeton.
Prior to his college graduation, he never boxed competitively, nor did he even train as a boxer. He claims that the only boxing he did before graduating from college was with his brother Mike in their parents' basement when growing up, in which they used rags to cover their hands.
He went to A.I. du Pont High School in Greenville, Delaware. Milligan is now the head coach of the Varsity wrestling team at Wilmington Christian School in Hockessin, Delaware.
After college, Milligan worked as an engineer at Delmarva Power and Light Company in Wilmington, Delaware, not far from where he grew up. At that time, he decided to try his hand at boxing.
Despite having no prior background in boxing, Milligan had an outstanding amateur career, and in 1983 he won the National AAU Heavyweight Championship. Being a white, Ivy League educated boxer attracted a lot of attention to him, and he was featured in numerous newspaper and magazine articles nationwide, including People Magazine and Sports Illustrated. He also defeated Henry Tillman, the 1984 Olympic Heavyweight Gold Medalist, in the 1983 National finals in Colorado Springs, Colorado.
He entered the 1984 U.S. Olympic trials seeded first in the 201 pound class, despite weighing only 184 pounds, but lost in the semi-finals to 17-year-old Mike Tyson on June 9, 1984. Milligan was leading on points when Tyson stopped him in the second round.
Milligan turned pro in 1985 and began his career with a promising string of 11 victories, but then lost a couple of bouts, retiring in 1986. He launched two comebacks in which he fought in local bouts, and fought for the WBO Cruiserweight Championship of the World in December, 1993 in Aspen, Colorado, losing on a cut in the eighth round, and retired permanently in 1998.
Milligan has appeared in ten national television commercials and a feature film with Robert De Niro and Jessica Lange, titled Night and the City (1992 film). He is the president of the Elsmere, Delaware Boxing Club, a civic member of the Mary Campbell Center for Disabled Adults and the Delaware Foundation for Retarded Children. In 1993, Milligan was inducted into the Delaware Sports Museum and Hall of Fame.Milligan is now the head coach of the Varsity wrestling team at Wilmington Christian School in Hockessin, Delaware.
He is a member of Mensa International, which requires that all members have IQ's that place them in the top 2% of the population, and the Triple Nine Society (99.9% IQ).