Bill "Mosie' Mosienko grew up in the north end of Winnipeg with nine brothers and four sisters. He began his hockey career at the age of ten in the Winnipeg Minor Hockey system with Tobans Athletic Club and later the Sherburn Athletic Club before graduating to the junior ranks with the Winnipeg Monarchs in 1939-40.
He turned pro with the Chicago Black Hawks at the age of 18 and was sent to the minors for seasoning. Mosienko split the next two seasons between the NHL and the minors before earning full-time duties with the Black Hawks in 1943.
Mosienko was teamed on a line with Clint Smith and Doug Bentley in 1943-44 and this threesome went on to set an NHL record of amassing 219 points. The record was broken by one point the following season by three fellows from Montreal named Blake, Lach, and Richard. Mosienko recorded four assists in the third period in a game against the Montreal Canadiens in 1945 and won the Lady Byng Trophy at season's end, in addition to a berth on the NHL Second All-Star Team.
He was teamed with Doug Bentley and Max Bentley to form the famous "Pony Line" in 1945-46 and was selected to the NHL Second All-Star Team for the second consecutive season. In all, he played in five league All-Star games during his 14-year NHL career including the 1947 All-Star Game in Toronto where Jim Thompson of the Leafs broke Mosienko's ankle causing him to miss the first two months of the season.
Mosienko will always be remembered for his record three goals in 21 seconds scored against goalie Lorne Anderson of the New York Rangers on March 23, 1952. Linemate Gus Bodnar assisted on all three, and all of the goals were scored while the teams were at even strength.
Mosienko suited up for the Winnipeg Warriors of the WHL in 1955-56 and helped the team win the league championship. He was named to the WHL's All-Star Team in the 1957, '58, and '59 seasons and was named Manitoba's Athlete of the Year in 1957. He retired for good in 1959 but coached the Warriors the following year before turning his attention to Winnipeg Minor Hockey, the Manitoba Oldtimers, and the Hockey Players Foundation, as well as playing in annual golf tournaments.
In 1980, he was inducted into the Manitoba Sports Hall of Fame and to the Manitoba Hockey Hall of Fame in 1985. In 1991 the City of Winnipeg re-named the Keewatin Arena as the Bill Mosienko Arena, and in 1965 he was inducted into the Hockey Hall of Fame.