His career started from the local team of Kastoria in 1994 when he was 14 years old. In 1999 he moved to Thessaloniki and he was transferred to the team of Iraklis. There, from his second season at the team of Iraklis, he won a position in the men team and helped a lot the team to return to the old accomplishments. With Iraklis, Dimitris Diamantidis won the title of the most valuable player of the Greek Championship for the season 2003-04.

In 2004 his trasfer to Panathinaikos took place. With Panathinaikos he is crowned 9 times Champion of the Greek Basketball League (2005, 2006, 2007, 2008, 2009, 2010, 2011, 2013, 2014), 8 times winner of the Greek Cup (2005, 2006, 2007, 2008, 2009, 2012, 2013, 2014) and 3 times European Champion (Euroleague) (2007, 2009 and 2011).

After his trasfer to Panathinaikos he has achieved several personal distinctions. At the Greek Championship he won the MVP title for 4 times (2006, 2007, 2008 and 2011) and 3 times in a row won the MVP title at the Greek Championship playoffs (2006, 2007 and 2008). Another distinction as MVP came in 2009 at the final of the Greek Cup as well with several participations at the Greek All Star Games (2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011 and 2013).

Additionally, he was voted as best Euroleague defense player 6 times, 5 in a row (2005, 2006, 2007, 2008, 2009) and in 2011. He was also voted as MVP Euroleague Final 4 in Athens (2007) and in Barcelona (2011) and he also won the title of the best European player for 2007 (Mr. Europa European Player of the Year 2007). Moreover, in 2011 he was voted as Euroleague MVP and 2 times selected for the best 5 of Euroleague in 2007 and in 2011).

Dimitris is a main stem of the Greek National Team since 2001, with which he won the gold medal at Eurobasket 2005 in Belgrade (1st in assist). Also, he won the silver medal at Mundobasket 2006 in Japan and the same at Mediterranean Games in Tunisia 2001. Furthermore he participated at the Olympic Games in Athens 2004.