On 26 October 2016, Kjartansson won the Swedish championship as Malmö FF sealed the title in his absence.

[11] He played 16 league games and scored one goal during the first half of the season, as Rubin Kazan was placed 13th in the table, before terminating his loan deal on 11 January 2020.

[16] Viðar made his senior international debut for Iceland in 2014, starting as a centre forward in a friendly against Austria.

[20] Viðar once again missed out on playing in an international championship, when he was left out of Iceland's World Cup 2018 squad, serving as a non-squad reserve.

[21] Viðar announced his retirement from international duty in October 2018 at the age of 28, having won 19 caps and scored two goals.

[22] In March 2019, Viðar reversed his decision to retire from the national team and was called up to represent Iceland in the UEFA Euro 2020 qualifying games against Andorra and France.