Jansen signed for the American side Washington Diplomats in 1980, but after playing 27 games for them, he returned to the Netherlands to sign for Ajax, on the advice of Johan Cruijff, who played together with Jansen at the Washington Diplomats.
Jansen would play as libero and fill a gap in the Ajax defence after the departure of Krol in the summer of 1980. By November 1980, after 13 rounds of the Eredivise Ajax were 8th, by the end of the season they had picked up form and finished as runners-up behind AZ and in front of FC Utrecht. The next season Ajax went on to win the Eredivisie with Jansen in the team. Feyenoord fans didn't like former player Jansen playing for their main rivals Ajax. On his Ajax debut (which, incidentally, was away to Feyenoord. Ajax lost 4–2) a snowball was thrown at his eye and Jansen had to leave the field for treatment. Jansen stayed at Ajax until summer 1982 when he retired.
He began his management career at his old club Feyenoord, where he worked as a coach, and then as assistant manager, between 1983 and 1987. After a season as manager of Belgian club SC Lokeren, he was appointed as Technical Director at second division SVV, where he won the league alongside his manager – future Rangers manager Dick Advocaat.
In 1991, he returned to Feyenoord as manager, winning the Dutch Cup in 1991 and 1992 and taking them to the semi-finals of the European Cup Winners Cup in 1991/92. He became Technical Director in 1992, with Hans Dorjee being appointed as manager, but Dorjee became ill and Jansen took over as manager again. Dorjee later resigned and was replaced as manager by Jansen's old teammate, Willem van Hanegem. Feyenoord won the Dutch Championship in 1993 and the Dutch Cup again the following season, but after a dispute with the executives of the club, Jansen left to work as assistant manager of Saudi Arabia alongside Leo Beenhakker. Between 1994 and 1997 he also managed Japanese side Sanfrecce Hiroshima.
On 3 July 1997, Wim Jansen was appointed as head coach of Celtic, replacing the sacked Tommy Burns. He went on to guide them to their first Scottish league championship in 10 years, ending the hopes of rival Rangers to win a tenth consecutive championship. Despite winning the league and the Scottish League Cup during his only season in charge, Jansen left the club less than 48 hours after the title was secured due to a personality clash with general manager Jock Brown. His most notable transfer was the signing of Henrik Larsson from Feyenoord.
At the beginning of the 2008/2009 season Jansen took up the position of assistant to the head coach of the Feyenoord first team, Gertjan Verbeek.
^At the time of Jansen's tenure in Japan, the result of a J-League match could not be a draw. In the event of scores being level at the end of 90 minutes, matches would be decided by extra time and penalties.