Karner started his career in 2005 in
Red Bull Salzburg. In 2010, he moved to
SV Ried, but in the same year he was loaned to
SV Grödig. In June 2011 he came back to
SV Ried. In 2013, he signed one-year deal with
SV Grödig. On 6 July 2015, Karner signed two-year deal with
Levski Sofia in
Bulgaria. He made his Levski debut against
Botev Plovdiv on 18 July, starting as a centre back in a 1–1 league draw. On 19 August 2016, Karner signed a short-term deal until the end of the season at
Derry City where he linked up with former teammate
Lukas Schubert. He made his debut for the club in a 2-2 draw with
Bray Wanderers at the
Carlisle Grounds on 27 August 2016. ==Statistics==