Leif Hansen debuted as an amateur boxer in 1945, and boxed for the club Sportsklubben 09, which was situated on the east side of Oslo, Norway. Already as a young man he became an East side legend with his nickname "Baggis." He boxed in the classic up-right British style.
He worked as a jockey in the years after the World War II.
Hansen participated in the European Championships in Oslo 1949, at Bislet Stadium, but was outpointed by the Finn Leo Lindberg in the first series. Hansen was selected for the European team against United States Golden Gloves in 1951 and lost on points to Bobby Bickle in Chicago March 29. In the Helsinki 1952 Olympic Games, he met the winner-to-be Chuck Adkins in the first series and was stopped by TKO in the first round. Hansen won the Norwegian National lightweight titles in 1951, 1952, 1953, 1954, and 1955.
Besides his amateur career, which many Oslo citizens followed, Hansen ran a successful carpet business, covering many a floor with linoleum in the apartments of Oslo's new suburbs where he himself came to live.
He was active in the Social Democratic Party and had his say in the fields of sport and youth activities.
After retiring from the amateur scene in 1955, with 323 fights, Leif Hansen turned pro under Edwin Ahlquist in Sweden with two fights in 1956.
Some of his money he invested in pro boxing, bringing the sport back to Norway. He promoted eight shows from 1957-1959, sixteen shows from 1964-66, and three shows in 1971. He fought as a pro on eight of this cards. In later years, he often spoke with bitterness about his shortlived business ventures in boxing, but on his 65th birthday, the boxing community in Norway honored him with a nostalgic show in Oslo where his team-mates gave homages and some of his former pros boxed exhibition bouts.
Leif "Baggis" Hansen died in Oslo 2004.