Jóhannes was born and raised in Iceland, but spent a few years of his childhood living on the Faroe Islands with his mother. He fluently speaks Icelandic, Faroese, Danish and English. He graduated with a BFA degree in acting from the Iceland Academy of Arts in 2005 and has been working in theatre, television and films since.

He has extensive experience in theatre in Iceland and was a resident artist at the National Theatre until he started working in international television and film projects. His first international film role was in Darren Aronofsky's 'Noah', as Cain (the world's first murderer).

His first international television role was on NBC's 'A.D: Kingdom And Empire' as the Apostle Thomas. His TV credits also include Game of Thrones and BBC's The Last Kingdom.

Notable features include Alpha (2018), Atomic Blonde, The Good Liar and The Sisters Brothers.