Pratt was considered one of the best defensemen of his day when began his NHL career in 1935.

Pratt played eight seasons with the New York Rangers from 1935-43, winning the Stanley Cup in 1940. The Rangers traded Pratt to the Toronto Maple Leafs for defenseman Red Garrett and forward Hank Goldup on Nov. 27, 1942. Pratt played for Toronto through the 1945-46 season, then was traded to the Boston Bruins. He played 31 games with the Bruins in 1946-47 before he was assigned to the minors.

Pratt won the Hart Trophy as NHL MVP in 1944, becoming the fourth NHL defenseman to do so (Herb Gardiner with the Montreal Canadiens in 1927; Eddie Shore with the Bruins in 1933, 1935 and 1936; and Ebbie Goodfellow with the Detroit Red Wings in 1940). The Hart honor came in his second season with the Maple Leafs, when he scored 58 points (17 goals, 41 assists) in 50 games.

Pratt helped Toronto win the Stanley Cup in 1945, his second championship. He had 293 points (83 goals, 210 assists) in 518 NHL games.

Pratt was also known to have an affable personality. In his 2013 book, "We Are the Rangers," Stan Fischler devoted the chapter "The Most Colorful Ranger" to Pratt, comparing him to Brooklyn Dodgers star Babe Herman, "a formidable hitter whose ability was often overshadowed by his zany antics. And that was the story of Babe Pratt's hockey life."

Pratt was inducted into the Hockey Hall of Fame in 1966. He had several jobs with the Vancouver Canucks, first in public relations when the Canucks entered the NHL in 1970, and later as a goodwill ambassador. He also was an analyst for "Hockey Night in Canada" broadcasts from Vancouver in the 1970s. Pratt died of a heart attack he had while attending a Canucks game Dec. 16, 1988. He was 72. The Canucks renamed their Premier's Trophy in Pratt's honor beginning in 1989; the award is given annually to the best Vancouver defenseman each season, as voted by the fans.

Pratt's son, Tracy, had a 10-season career as a defenseman in the NHL (1967-77).