[4] He played in his first Junior Grand Slam event at Wimbledon in 1977 and made his debut in a senior tournament at the Swedish Open.

[4] Simonsson also made his Davis Cup debut for Sweden during July 1979 in the Europe Zone B, semifinals against Romania.

In the singles, he defeated Georges Goven in the final and in the doubles, he teamed with compatriot Anders Järryd to win the title.

[4] During May 1982, Simonsson made his first final on the Grand Prix tennis circuit at the tournament in Florence, where he lost in three sets to the world number 9 Vitas Gerulaitis.

[4] At the Bordeaux Open he was successful in the doubles and won his first Grand Prix title with fellow Swede Magnus Tideman.

In November and alongside Stanislav Birner, he played in his second doubles final at Ferrara, and the following week, he and Jan Gunnarsson reached the semifinals in Toulouse.

[4] In 1986, Simonsson reached one quarterfinal on the Challenger Tour at Marrakesh, and he played his last singles match at Kitzbühel, losing in the first round.