In the 2000–01 season, Friedrich signed his first professional contract. Hermann Gerland, head coach of Arminia Bielefeld at the time, scouted Friedrich while playing for Regionalliga club SC Verl. Because of his convincing performance, Gerland decided to bring Friedrich to Bielefeld, where he immediately became a regular starter.
Hertha BSC
In 2002, he accepted an offer from Hertha BSC. With the Berlin club, Friedrich won the DFB-Ligapokal that year, defeating FC Bayern Munich, Borussia Dortmund, and FC Schalke 04. In 2004–05, Falko Götz named Friedrich captain, a role he kept for the remainder of his time at Hertha. He renewed his contract with Hertha twice which was due to run until 2012 with a performance-based option for an additional year. He made 231 matches in the German top-flight for the club from the capital.
However, after Hertha's relegation in 2010, he left the club in a €2million transfer to VfL Wolfsburg, signing a three-year contract. On 19 September 2011 he was released from his contract at Wolfsburg due to long term injury.
In March 2012, he signed with the Chicago Fire of Major League Soccer. Friedrich made his competitive debut for Chicago in a match against the Houston Dynamo on 16 April 2012. The game ended in a 1–1 draw. Friedrich scored his first MLS goal on 12 August 2012 in a match against Philadelphia Union. Friedrich was named the club's 2012 season's Defender of the Year. At the end of 2012 season, Friedrich extended his contract with Chicago Fire until the end of 2013. Due to recurring injuries, Friedrich did not appear in any matches in 2013.
Retirement
On 23 June 2013, Friedrich announced his retirement from professional football.
International career
Friedrich played a total of five games for the German U-21 team, and once for the B-team known as "Team 2006". in 2009 On 21 August 2002, Friedrich made his debut for the senior team against Bulgaria with in a 2–2 draw in Sofia. His first major tournament for the national team was Euro 2004 where he appeared in all three group matches that saw the German team was eliminated. On 21 December 2004, Friedrich captained Germany in a 5–1 friendly win over Thailand in Bangkok. He has captained the team three more time since. In 2005, Germany took part in the Confederations Cup, as upcoming World Cup hosts. Friedrich took turns with Andreas Hinkel on the right wing back position. The following year, he was part of the 23-man squad for the 2006 World Cup. Except the match for third place, which he missed due to an injury, Friedrich started all of Germany's games. At Euro 2008, Friedrich was once again part of the German team, but was initially intended as a substitute. Following an injury to Marcell Jansen, he started the final group game and all three knock-out stage matches. The quarter-final was one of Friedrich's best international matches where he successfully shut down Portuguese star Cristiano Ronaldo. In March 2009, German coachJoachim Löw explained that he now planned Friedrich as a centre back instead of the right wing back position. He was part of Germany's squad in the 2010 World Cup in South Africa. After a Bastian Schweinsteiger solo run, he scored his very first international goal on his 77th appearance for Germany on 3 July 2010 in the 2010 World Cup 4–0 quarter-final win over Argentina.
After retirement
On 28 August 2014 it was confirmed, that Friedrich was the new assistant coach of the German U18 national team. He left the position at the end of 2015. On 27 November 2019, Friedrich was hired as a performance manager at Hertha BSC under manager Jürgen Klinsmann, who was hired earlier on the same day.
