During his career, he won seven Grand Slam singles titles and one Grand Slam doubles title. He is particularly remembered for his most dominant year on the tour, 1988, when he won three of the four Grand Slam singles events. He was also a driving force behind Sweden's run of seven consecutive Davis Cup finals in the 1980s. He has four children: Emma, Karl, Erik, and Oscar.

He first came to the tennis world's attention as a brilliant junior player, winning the French Open junior title, the European under-16 and under-18 championships, and the prestigious Orange Bowl under-16 event in Miami. He made his debut on the professional tour in 1981.

Wilander shocked the tennis world in 1982, upsetting Guillermo Vilas in four sets in the final to win the French Open and become the youngest-ever male Grand Slam singles champion at 17 years, 9 months. (This record has since been broken by Boris Becker and Michael Chang.) Wilander won three further tournaments in 1982, to finish the year ranked the World No. 7.

Wilander was back in the French Open final again in 1983, where he lost to Yannick Noah. He won his second Grand Slam title later that year at the Australian Open, played on grass courts at Kooyong, where he defeated John McEnroe in semi-finals and Ivan Lendl in the final. He won nine other tournaments in 1983 to finish the year ranked as the World No. 4.

Wilander retained his Australian Open title in 1984, beating Kevin Curren in the final. In 1985 he won the French Open for the second time, beating Lendl in final, and again reached the Australian Open final, where he lost to his compatriot Stefan Edberg. He rose to the World No. 2 ranking, behind Lendl, early in 1986. But the No. 1 ranking still proved elusive. Wilander was defeated by Lendl in the final of both the French Open and the US Open in 1987.

1988 was the pinnacle of Wilander's career. In January, he won his third Australian Open, this time on Flinders Park's hardcourts, after a spectacular five-set final against home-crowd favourite Pat Cash. In doing so, he became the only player ever to win the Australian Open on both grass (twice) and hardcourts. After that he faced another home-crowd favourite, Henri Leconte, in the final of the French Open and won in straight sets. At Wimbledon, he reached the quarter-finals where he lost to Miloslav Mecir. At the US Open, he reached his third Grand Slam final of the year. In a repeat of the previous year's match-up, he would face Lendl in the final, and a win would allow Wilander to end Lendl's three-year reign at the top of the world rankings. After a fantastic five-set battle, lasting almost five hours, Wilander claimed his seventh Grand Slam title and the World No. 1 ranking, having won three of the year's four Grand Slams and three Mercedes Super 9 titles (Miami, Cincinnati and Monte Carlo) and one other title. He held the No. 1 ranking for a total of 20 weeks through the end of January 1989.

His 1988 title at Cincinnati was his fourth there, making him one of only three players since 1899 to win four titles in Cincinnati: the other two are fellow International Hall of Famers Bobby Riggs (who won titles in 1936, '37, '38 and '40) and George Lott (1924, '25, '27 & '32).

Wilander was an integral member of Sweden's highly-successful Davis Cup team throughout the 1980s. He reached his first final with Sweden in 1983, where they lost 3–2 to Australia (despite Wilander winning both his singles rubbers in the final). In 1984, Sweden (with Wilander) won the cup, beating the United States 4–1 in the final. They retained the cup in 1985, with a 3–2 final victory over West Germany. Wilander helped Sweden reach the final again in 1986, but declined to play in the final because he was getting married (Sweden lost 3–2 to Australia). Wilander played in his fourth final in 1987, where Sweden beat India 5–0. Two more finals followed in 1988 and 1989, but Sweden lost both to West Germany. Wilander compiled a 36–14 record in singles and a 7–2 record in doubles in the Davis Cup for Sweden. However, Wilander's most memorable Davis Cup match came in defeat. In a 1982 quarter-final tie against the United States, Wilander was defeated in a five-set, 6 hour and 32 minute marathon by John McEnroe (7–9, 2–6, 17–15, 6–3, 6–8). It remains the longest match in Davis Cup history.

Wilander won a total of 33 singles titles and seven doubles titles during his career.

The only Grand Slam singles title Wilander never won was Wimbledon. However he did capture Wimbledon's men's doubles title in 1986 (partnering countryman Joakim Nystrφm).

Because two of his Australian Opens were won on grass, Wilander is one of the few players to have won Grand Slam titles on grass, hard, and clay courts.

Wilander retired from the professional tour in 1996. He now spends much of this time living in Hailey, Idaho (part of the Sun Valley ski resort) with his wife Sonja (nee Mulholland), a South African-born model. He competes from time-to-time on the senior tour. Since retiring as a player, he has served as captain of the Swedish Davis Cup team and as coach of the Russian player Marat Safin. He also occasionally spends time commentating tennis matches on Eurosport. In 2002, he was inducted into the International Tennis Hall of Fame in Newport, Rhode Island, USA.