From 1999 till 2018 he was the drummer for the band Sigur Rós, which he joined in 1999, shortly after the recording of the studio album Ágætis byrjun, when the previous drummer, Ágúst Ævar Gunnarsson, left the band.

[1][2] Orri has recorded five studio albums with Sigur Rós: ( ) (2002), Takk... (2005), Með suð í eyrum við spilum endalaust (2008), Valtari (2012), and Kveikur (2013).

Orri's father is the former footballer Dýri Guðmundsson, who made five appearances for the Icelandic national team.

He is married to María Lilja Þrastardóttir, a journalist and a feminist activist from Iceland.

[7][8] Orri published a post on Facebook where he claims his innocence but "in light of the scale of this matter" he chose to step down from the band whilst attempting to clear his name.