Throughout his career, he has played for Bayern Munich, Newcastle United, Liverpool and Manchester City primarily in a defensive midfield position.

He is highly respected by supporters of Liverpool due in large part to his involvement in the club's victory in the 2005 UEFA Champions League final.

He resigned from the post on 7 November 2011 after only four months with Stockport struggling in 17th place in the Conference Premier citing failure of a proposed takeover by Tony Evans.

[3] Hamann joined a team led by Lothar Matthäus, Thomas Helmer, Christian Ziege and Oliver Kahn and played five games, mostly as a right winger.

In the next season, Bayern suffered a major injury wave which claimed midfielders Matthäus, Swiss international Alain Sutter, talent Dieter Frey and veteran Markus Schupp, which allowed Hamann to become a regular; he played 30 Bundesliga games[3] and established himself as a valuable role player, playing either right wing or defensive midfield.

He earned himself a full professional contract and was an important player in the tumultuous 1995–96 campaign, in which Bayern recruited striker Jürgen Klinsmann, coach Otto Rehhagel and midfielders Andi Herzog, Thomas Strunz and Ciriaco Sforza, but the team was torn apart by heavy internal struggles.

After being a bench player most of his career until then, new coach Giovanni Trapattoni made him a starting defensive midfielder, and new recruit Mario Basler took the right wing.

[3] In his private life, Hamann had to overcome a scary period when he broke down unconscious and was diagnosed with a stroke, but made a full recovery.

[7][8] Hamann also played the full 90 minutes and assisted Liverpool's second goal (scored by Michael Owen) in the team's 2-0 victory over Manchester United in the 2003 Worthington Cup final.

Although he was suffering a broken toe during the final,[10] Hamann's substitution for Steve Finnan at half time was the catalyst for Liverpool's historic fightback.

Earlier in the tournament, Hamann had been forced to stand in for Liverpool's key player Steven Gerrard in the first leg of the last 16 round against Bayer Leverkusen.

[17] However, on 28 August 2013 during Colin Murray's morning radio show with TalkSport Bolton Wanderers chairman Phil Gartside announced that the club had never officially signed the midfielder and that they had "put (the papers) in the drawer".

A Premier League investigation found that this wasn't the case and that Bolton had indeed signed Hamann, and expressed confusion as to why Gartside had lied about it.

After retiring in February 2011 and managing Stockport County in July 2011, Hamann went back to playing football, and this time for amateur-side TuS Haltern.

During the group stage, Hamann drifted in and out of the starting XI, finally breaking into the team when Germany gained momentum in the second round game against Mexico.

[26][27] Alongside Michael Ballack and Bernd Schneider, Hamann was one of the key players in Germany's surprising run to the 2002 FIFA World Cup Final.

He became only the second Liverpool player after Roger Hunt in 1966 to play in a World Cup Final while still at the club, but finished on the losing side as Brazil won 2–0 in Yokohama.

In the 2–2 draw against the Netherlands, Hamann produced a lacklustre performance, apparently convincing Klinsmann that he did not possess the required pace for that kind of level anymore.

[22] On 5 July 2011, Hamann was appointed as the new manager of newly relegated Conference Premier club Stockport County, replacing Ray Mathias.

Hamann resigned as Stockport County boss on 7 November 2011, citing the failure of the proposed takeover by Tony Evans to materialise; his team were languishing in 17th place having taken only three wins from his nineteen league games in charge.

He was again part of RTÉ Sport's studio coverage for the finals of UEFA Euro 2016,[39] beginning with an appearance for the opening night match between tournament hosts France and Romania.

He released his autobiography, The Didi Man: My Love Affair with Liverpool, co-written with Malcolm McClean, in February 2012 and it became a Sunday Times Best Seller.