Neustädter began his career in 1. FSV Mainz 05’s youth team, before being promoted to Mainz 05 II in July 2006. After playing in Mainz’s first team during the 2008–09 season, he signed a three-year contract with Borussia Mönchengladbach. With die Fohlen, Neustädter enjoyed a particularly successful 2011–12 season, finishing fourth and qualifying for the 2012–13 UEFA Champions League.

Neustädter played twice for Germany U-20, making his debut as a substitute against Italy U-20 on 9 April 2008. He scored a goal against Switzerland U-20 on 22 April 2008.

On 9 November 2012, Neustädter was called up for the Germany squad to face the Netherlands in a friendly match five days later. He made his debut for Germany in this match as a late substitute for Schalke team-mate Lewis Holtby.

On 30 May 2016, Neustädter was granted Russian citizenship, having received his new Russian passport at the Russian Consulate in Bonn.

In July 2016, after turning down a new contract at Schalke, Neustädter signed a three-year deal at Fenerbahçe S.K. of Turkey.

In January 2016, Neustädter met with members of the Russian Football Union in order to be able to possibly play for the Russia national team in the future. On 21 May 2016, he was called up to represent Russia at UEFA Euro 2016. On 1 June 2016, Neustädter made his debut for Russia, in a 2–1 friendly loss to the Czech Republic, as a 64th-minute substitute. He started Russia’s first two games during the final tournament in France, where Russia failed to proceed through the group stage.

On 11 May 2018, he was included in Russia’s extended 2018 FIFA World Cup squad. He was, however, not included into the final World Cup squad.

On 9 August 2019, he signed a one-year contract with Russian club FC Dynamo Moscow. On 15 October 2020, after the first 10 games of the 2020–21 Russian Premier League were played, he returned to Dynamo until the end of the season.