In 1994, along with Mats Näslund and Håkan Loob, Tomas Jonsson became one of the first three members of the Triple Gold Club, players who have won a Stanley Cup, a World Championship and an Olympic gold medal. A defender, Jonsson started his hockey career with Falu IF in 1974. In 1977 he moved to MoDo AIK and won the Swedish title with them in 1979. Jonsson had been drafted by the New York Islanders of the NHL in 1979 and joined the team in 1981. With the Islanders, Jonsson won the Stanley Cup in 1982-83 and played with them until 1989, when he was traded to the Edmonton Oilers in mid-season. After half-a-season with the Oilers, Jonsson returned to Sweden and finished his career with Leksands IF from 1989-98. He was awarded the Goldpucken Award as the best player at the 1995 Swedish championships and was selected to the Swedish Championships all-star team in 1979, 1980, 1990 and 1995.
Internationally, Jonsson was capped 203 times with the Swedish national team. He won an Olympic gold in 1994 and bronze in 1980, was World Champion in 1991, while winning silvers in 1981, 1986, 1990 and 1995 and bronze in 1979. He also won a European title in 1990, winning silvers in 1981, 1986 and 1991 and bronze in 1979. As a junior, Jonsson was European junior champion in 1977 and won World Junior Championships silver in 1978 and bronzes in 1979 and 1980. He was awarded the Stora Grabbars Märke (Big Boys’ Badge) #110 in ice hockey and was selected to the IIHF Hall of Fame in 2000. After finishing his playing career, Jonsson worked as an ice hockey coach, coaching the Swedish national junior team, Falu IF, Leksands IF and Brynäs IF. He was also an assistant coach of the Danish national team.