He was offered a scholarship to the University of Alberta, but decided to quit football after he began learning how to box at a Grande Prairie health club which was run by a man named Jim Murrie.

Impressed with his dedication and size, Murrie introduced deWit to Dr. Harry Snatic, a dentist and rancher who had been a youth boxing coach in Louisiana before moving his family in 1971 to Beaverlodge, a small town near Grande Prairie.

[citation needed] In 1987, DeWit lost his father, Len de Wit, and younger brother, Theo, who was 23 at the time, in a plane crash that killed 4 people in total.

Snatic then entered deWit in the British Columbia Golden Gloves championships where he fought 18-year-old Shane Anderson who was the western Canadian 178-pound champion and a veteran of about 40 fights.

deWit went with him in order to find sparring partners, and to train with a Ugandan exile named Mansoor Esmail, who was Calgary's top boxing coach, and was considered a physical conditioning genius.

DeWit's first major victory came in Las Vegas in June 1982 when he knocked out Cuba's Pedro Cardenas to win his first North American title.

Leading up to the 1984 Olympics, a benefit in Calgary featuring boxing fan Ryan O'Neal and Farrah Fawcett raised $70,000 to finance DeWit's training.

Tabbed early as a "Great White Hope," deWit turned professional immediately, persuaded in part by a contract offer reportedly worth $1 million and began to train out of Burnet, Texas.

[5][6] A loss to Bert Cooper in 1987 was deWit's only career defeat, as he retired after five consecutive wins, the last of which being a unanimous decision victory over Henry Tillman.

In 2012, deWit made a cameo appearance in the Calgary-based Souls in Rhythm band's musical video Another Round (featuring hop-hop artist Transit).