[1] Karhan started and finished his career at Spartak Trnava; in between, he played in Spain, Turkey and Germany, where he spent ten seasons.

Karhan was a regular member of the Slovakia national team and with 107 appearances, played the second most matches of any player to represent them.

[6] In August 2013, Karhan announced his retirement from professional football and that he moved to a role of sports director of Spartak Trnava.

[6] Karhan made 107 appearances for Slovakia for 16 years,[clarification needed] being the most-capped Slovak footballer of all time,[3] until his record was surpassed by Marek Hamšík in October 2018.

[4] Karhan is the father of two boys: Patrick, who currently plays for Spartak Trnava and represented Slovakia at youth international level, and Alex Thomas.