Royer began his career as a youth player at FC Schladming in Upper Styria, where he was active from 1996 to 2004. In 2004, he moved to Sturm Graz. He quickly moved up the club's youth system and played for the club's reserve team during the 2008–09 season making 12 appearances and scoring two goals. Royer joined Regionalliga team Pasching during the 2009–10 season. In his one season at the club he appeared in 25 league matches scoring six goals. After impressing with Pasching, Royer began to receive interest from Austrian Bundesliga clubs.
Royer signed with Ried in 2010. On 10 October 2010 he scored his first goal for Ried in a 3–0 victory over LASK Linz. The following match day, on 6 November, Royer scored the winning goal for Ried in a 2–1 victory over Austria Wien. He ended his first season at the club capturing the Austrian Cup. Royer began his second season with Ried before transferring to German club Hannover 96 on 31 August, the last day of the transfer window.
For the 2012–13 season Royer was sent on loan to 1. FC Köln. On 26 August 2012, Royer he scored his first goal for Köln in a 3–3 draw with Kaiserslautern. In his one year at the club Royer was a regular for Köln as he appeared in 26 league matches and scored 3 goals.
Austria Wien
On 24 June 2013, Royer returned to Austria, signing with Austria Wien. He scored his first goal for Austria Wien on 25 August 2013 opening the scoring for his club in a 4–1 victory over Wolfsberger AC. Royer was an important player for Wien, in his two seasons at the club he made 76 appearances, scoring 14 goals.
Midtjylland
On 22 May 2015, Danish champions FC Midtjylland announced the signing of Royer. Royer scored his first goal with Midtjylland on 10 August 2015 in a 2–0 league victory over AaB. During the 2015–16 season he appeared in 36 matches scoring two goals across the Superliga, Champions League qualifying, and Europa League.
New York Red Bulls
On 3 August 2016, Royer signed with New York Red Bulls. On 21 August 2016, he made his New York Red Bulls debut at RFK Stadium against D.C. United in a 2–2 draw. He scored his first goal with the club on 24 September 2016 in a 1–0 victory; heading in the winning goal against the Montreal Impact. On 27 May 2017, Royer scored the game-winning goal in a 2–1 victory over New England Revolution. On 14 June 2017, he scored the lone goal for New York in a 1–0 victory over rival New York City FC in the 2017 Lamar Hunt U.S. Open Cup. On 19 July 2017, he recorded his first multi-goal game for New York, scoring twice in a 5–1 victory over San Jose Earthquakes. Three days later, Royer scored the opening goal and assisted on another in helping New York to a 3–0 victory over Minnesota United, earning him MLS Player of the Week honors. On 29 July 2017, he scored another two goals for New York in a 4–0 rout over Montreal Impact. On 22 February 2018, Royer scored New York's lone goal in a 1–1 draw against CD Olimpia in the first leg of the round of 16 match of the CONCACAF Champions League. On 28 April 2018, he scored his first league goal of the season, helping New York to a 3–2 victory over Los Angeles Galaxy. On 6 June 2018, he scored a brace in two minutes to cap off New York's 4–0 derby win over New York City FC in the fourth round of the 2018 Lamar Hunt U.S. Open Cup. On 11 November 2018, Royer scored a brace to lift New York to a 3–0 playoff victory against Columbus Crew, sending New York to the eastern conference finals. On November 8, 2019, Royer was named the New York Red Bulls team MVP for 2019 after leading the team in goals and assists throughout the season.
International career
Royer has represented Austria serving as captain of the under-21 team appearing in 9 matches and scoring three goals. On 19 May 2011, he was called up to the full national team by Dietmar Constantini. He made his first appearance for the national team on 3 June 2011 coming on as a second-half substitute for Martin Harnik in a European Championship qualifier against Germany.
