Johnson was born in Munich, Germany. He is the son of an African-American serviceman and former basketball player who played in Germany, and a German-American mother. In 1991, he started playing soccer at local Sportfreunde München.

In the mid-1996, Johnson moved to the renowned youth ranks of 1860 Munich. Johnson was promoted to the first team of 1860 München in July 2006. He amassed 89 league appearances scoring four goals before transferring to VfL Wolfsburg on 14 July 2009. He scored his first goal for VfL Wolfsburg in a 2–2 draw at home to SC Freiburg. In July 2011, Johnson transferred to 1899 Hoffenheim.

On 25 August 2011, Johnson was called up to the United States national team by head coach Jürgen Klinsmann for friendly matches with Costa Rica (2 September) and Belgium (6 September). Johnson had represented Germany at youth level, but was eligible for a one-time switch to represent the United States at senior level due to new FIFA eligibility rules; however, he wound up not being able to play as the required paperwork was still pending.

On 11 November 2011, Johnson made his international debut for the U.S. as a substitute in a 1–0 loss to France. On 15 November 2011, Johnson made his first full international start against Slovenia and drew a penalty in a 3–2 win. He played in the FIFA World Cup qualifier on 12 June 2012 against Guatemala. Johnson earned his first mark for the USMNT notching the assist in the United States’ only goal in their 4–1 loss to Brazil on 23 June 2012. He scored his first national team goal on 1 June 2014 in a pre World Cup friendly against Turkey. Johnson started each of the United States national team’s three group stage matches in the 2014 FIFA World Cup as well as the Round of 16 matchup with Belgium. He secured his second national team goal on 13 November 2015 in a World Cup qualifying match against Saint Vincent and the Grenadines.

On 26 September 2012, Johnson scored in Hoffenheim’s 3–0 victory over VfB Stuttgart, their first win of the new campaign.

On 26 September 2012, Johnson scored in Hoffenheim’s 3–0 victory over VfB Stuttgart, their first win of the new campaign.

On 24 February 2014, it was confirmed that Johnson would join Borussia Mönchengladbach on a free transfer following the conclusion of the 2013–14 season.

On 24 August 2014, Johnson made his first league appearance for Borussia Mönchengladbach, coming on in the 72nd minute of the home match against VfB Stuttgart. On 13 September 2014, he made his first league start in a home 4–1 win over FC Schalke 04. He scored his first UEFA Champions League goal on 3 November 2015 against Juventus. He scored his first Bundesliga goal for Borussia Mönchengladbach on 1 March 2015 against SC Paderborn.

On 24 February 2014, it was confirmed that Johnson would join Borussia Mönchengladbach on a free transfer following the conclusion of the 2013–14 season.

On 24 August 2014, Johnson made his first league appearance for Borussia Mönchengladbach, coming on in the 72nd minute of the home match against VfB Stuttgart. On 13 September 2014, he made his first league start in a home 4–1 win over FC Schalke 04. He scored his first UEFA Champions League goal on 3 November 2015 against Juventus. He scored his first Bundesliga goal for Borussia Mönchengladbach on 1 March 2015 against SC Paderborn.

On 12 March 2019, Johnson spoke with United States national team head coach Gregg Berhalter about the possibility of returning to the national team. Johnson has not played for the United States national team since he started in a World Cup qualifying loss to Costa Rica in September 2017.