After graduating from University of Minnesota he served as an assistant coach for the team. Before signing a pro contract he was a salesman for a chemical firm and became a U.S. Citizen. He played two seasons for the Rochester Mustangs (USHL) between 1965-67 averaging over a point per game. Shortly thereafter he was the captain of the 1968 U.S. Olympic team.
Lou quickly got the reputation of being a good team man, adept at killing penalties. He made his NHL debut shortly after his Olympic adventure and appeared in two games for the Minnesota North Stars, an organization that he would stay in for over 20 years. During the 1968-69 seasons he had brief stints with the Memphis South Stars (CHL) and Cleveland Barons (AHL) before playing in the NHL for good.
During the 1971-72 season, North Stars coach Jack Gordon used Lou as a forward (right wing) for the first time in the NHL and Lou responded with a respectable 21 goals and 49 points. The next two seasons he scored 15 goals respectively 11 goals and developed into a fine checking forward who often was matched against the other teams top lines.
His offensive output was limited the last years until he retired in 1978. Lou played a total of 635 games and scored 225 points (68 goals and 157 assists). He also represented USA during the 1976 and 1977 World Championships.
During the 1977 tournament his play was criticized loudly by team USA coach John Mariucci, who had coached Nanne previously at the University of Minnesota. The usually mild-mannered Nanne charged his coach and the two men were soon trading punches on the bench in the middle of the game. Peace was restored by teammates but the fight erupted again right after the game, necessitating a mass intervention by players and officials.
The incident came as a shocker since both men were North Stars employees and longtime friends. Mariucci had been Nanne's coach at the U. of Minnesota and the two remained close friends when Nanne went on to play for the North Stars and Mariucci became one of the teams scouts.
When Nanne was named the coach and GM of the North Stars in February 1978, who did he name as his assistant GM? Mariucci of course. It was typical Nanne. "Sweet Lou from the Soo" held his GM position with the North Stars until 1988.
For his many contributions to hockey in the United States, Nanne was honored as a recipient of the 1989 Lester Patrick award.
In 2010 Lou Nanne released his autobiography: A Passion To Win