Nedomanský played for HC Bratislava of the Czechoslovak Extraliga for twelve seasons. In 1968 he was a member of the Czechoslovak national ice hockey team which won silver medals at the Winter Olympics in Grenoble and bronze medals in 1972 at the Winter Olympics in Sapporo. He also played for Czechoslovakia in nine IIHF World Championships, and was named top forward at the 1974 world championships He is manager of Slovak national team in North America.
Nedomanský defected in 1974 to Toronto via Switzerland. He was not able to return to his home country until after the fall of the Iron Curtain.
He played just over three seasons in the World Hockey Association with the Toronto Toros and the Birmingham Bulls, peaking with 56 goals and 98 points for Toronto in 1975–76. He also won the Paul Deneau Trophy for sportsmanship in 1975–76. He then signed as a free agent with the National Hockey League's Detroit Red Wings in 1977. Nedomanský played five seasons for Detroit, posting highs of 38 goals and 74 points. He retired after one final season with the St. Louis Blues and the New York Rangers in 1982–83.
Nedomanský coached in Germany during the 1987–88 season.