Jonker began his career with Vitesse '22 from his hometown
Castricum,
North Holland. From 1970, Jonker played eight years for
Telstar. After the club suffered relegation from the
Eredivisie in the
1977–78 season, he moved to
Den Haag alongside Ton Wickel. According to journalist Jan-Hermen de Bruijn, these signings meant that then head coach
Piet de Visser rejected the transfer of
Diego Maradona to Den Haag, as the club had enough midfielders. This was subsequently denied by De Visser, who stated that Maradona was already hugely popular in Argentina at the time, and would have cost too much for the club. Nevertheless, Jonker experienced his breakthrough at the club, and after two seasons in
The Hague, he signed with
AZ '67 in 1980 at the age of 29. The club from
Alkmaar was already a top club in the second half of the 1970s, but had not yet won the national title, and Jonker was a welcome reinforcement in midfield in 1980. Jonker played for AZ for three seasons and retired from professional football after the 1982–83 season, instead choosing to return to Vitesse '22 at amateur level. Jonker played 19 matches in the
European Cup on behalf of AZ '67, and was part of the successful team which convincingly won the Eredivisie with a goal difference of +71, and reached the final of the
UEFA Cup in the
1980–81 season, in which he scored in the return leg. He gained two caps for the
Netherlands national team, in which he played against
West Germany and
Cyprus. ==Honours==