Born in Villaviciosa, Asturias to an Icelandic father and a Spanish mother,[1] Johannesson joined Real Oviedo's youth setup in the 2011 summer, after spells at SD Llano 2000 and Sporting de Gijón.

On 3 September 2014, he made his first team debut, starting in a 4–0 Copa del Rey home routing of SD Amorebieta.

He made his professional debut on 25 October 2015, coming on as a second-half substitute for José Manuel Fernández in a 2–4 Segunda División away loss against SD Ponferradina.

On 14 June 2021, Johannesson signed a two-year contract with Albacete Balompié, freshly relegated to Primera División RFEF.

[7][8] Johannesson made his full international debut on 31 January 2016, replacing Guðmundur Þórarinsson at half-time in a 2–3 loss at the StubHub Center in Carson, California.