On 12 January 2012, it was announced that Birkir would sign for Belgian Pro League side Standard Liège on a five-year deal. He played 16 league matches in the Belgium Pro League for Standard.
After the end of the 2011–12 season, in July 2012, Birkir joined the newly promoted Serie A side Pescara on a season-long loan deal, for €300,000, with an option to sign for an additional €900,000. He scored his first goal for Pescara in a 5–1 away defeat at Napoli. After the 2012–13 season he stated that he was not interested in going down to Serie B with Pescara and, with two years remaining of his Standard Liège contract, he was unsure where he would be playing in the 2013–14 season.
He scored his first goal for Iceland against France on 27 May 2012 in a 3–2 defeat. He also followed this up with goals for Iceland in 2014 FIFA World Cup qualification with goals against Albania on 12 October 2012, Slovenia on 7 June 2013 and then against Albania again on 10 September 2013 in a 2–1 victory. Birkir's goals and performances played a crucial role in the qualifiers helping guide Iceland to the World Cup playoffs, however in November 2013 they lost 2–0 on aggregate over two legs to Croatia.