[1][2] After starting his career with KR[3] in 2010, Matthías Orri had is breakout season with ÍR in 2013–2014 when he averaged 16.8 points and 6.7 assists.

[4] After spending the 2015–2016 season with Columbus State University,[5][6] Matthías resigned with ÍR on 13 May 2016.

[9] In August 2021, Matthías stated that he was unsure if he would play for KR during the seasons as his passion for basketball had diminished considerably.

[16] Since his semi-retirement from playing, Matthías has worked as a basketball analyst at Stöð 2's Körfuboltakvöld and as a commentator at RÚV.

Matthías is the younger brother of professional basketball player Jakob Sigurðarson.