Arnar started playing guitar when he was 10 years old, recording his own songs on an old stereo. He formed his first band when he was 12 years old, a death-metal band called Inflammatory. Shortly after he fell in love with the Beatles and his death-metal carrier ended abruptly.

He studied classical singing for 4 years. In 2001 he formed a band called Leaves, who in the year 2002 released their debut album Breathe, receiving great reviews in magazines like NME, Q-magazine, Uncut and Rolling Stone. Title song 'Breathe' was used in an episode of OC (Orange County), and another song, 'Epitaph' was used in the Icelandic film Fálkar. Their second album The Angela test (2005) was released by Island records in the UK, and "We are Shadows was released in 2009.

Arnar was voted best male singer at the Icelandic Music Awards 2002.

Arnar is very prolific. He has composed and produced music to TV films and video art, worked with a huge selection of artists on various projects, and recorded and produced records for other artists, Tenderfoot and Kalli, to name but two.