Johansson competed in his first professional tour match in the 2000 Wideyes Swedish Open, where he retired against Markus Hipfl.
In 2001 Johansson focused on Challengers and only competed in one ATP tour tournament: the 2001 Stockholm Open, losing to Andreas Vinciguerra.
He also won his first ATP Tour level match in his home tournament in the 2002 Stockholm Open, defeating Albert Portas before losing to Fabrice Santoro.
In 2003 Johansson made his Grand Slam Debut in the 2003 Australian Open losing to American Mardy Fish.
He competed once again for the fourth straight year in the 2003 Stockholm Open where he reached his first quarterfinals where he defeated his first top 30 opponent, world no.
He followed it up with his first Grand Slam win in the 2004 Australian Open defeating Alexander Popp and Alberto Martín before losing to then world no.
Johansson continued his good form by winning his first ATP title in the 2004 Kroger St. Jude defeating en route James Blake, Mardy Fish and German Nicolas Kiefer in the finals.
However his good run was disrupted winning only two matches in his next seven tournaments defeating Mark Philippoussis and compatriot Robin Söderling.
He then went to the 2004 Wimbledon losing to Florian Mayer in the fourth round after defeating Arnaud Clément, Mardy Fish and Jonas Björkman.
Johansson began 2005 with a nice start winning in the 2005 Next Generation Adelaide International defeating Taylor Dent in the finals in two sets, reaching the fourth round of the 2005 Australian Open losing to Andre Agassi 7–6, 6–7, 6–7, 4–6 and winning the Open 13 event defeating Ivan Ljubičić in the finals which jumped him into the top 10 at number 9.
In 2006 he added physical rehabilitation and development practice with coach Agne Bergvall together with Swedish track and field stars Carolina Klüft, Susanna and Jenny Kallur.
In that match, Johansson fired 17 aces, and announced his return to the top of the game, calling it his "greatest win ever."
In his next tournament, the Madrid Masters, Johansson pulled off another upset in the second round, defeating fifth-seeded Nikolay Davydenko in three sets.
In 2007 Johansson only competed in 4 tournaments in the 2007 Next Generation Adelaide International reaching the Semifinals before losing to Novak Djokovic, 2007 Australian Open retiring in the first round to Guillermo García-López 1–1 in the first set.
He then underwent right shoulder surgery on 23 Feb. in Milan and did not return again until September for a Davis Cup SF tie against U.S. (l. to Roddick in opening rubber).
He then got a wildcard entry at the Malaysian Open and made a surprise win over Lleyton Hewitt in the first round before losing to Richard Gasquet.
In 2010, Johansson played his first match of 2010 in singles during the 2010 Davis Cup tie against Argentina, which he lost in four sets to Argentine Leonardo Mayer.