After spending the Autumn portion of the 2005–06 season with Auxerre, in January 2006, Diaby signed with English club Arsenal on a long-term contract for an undisclosed fee.

Of Ivorian descent, Diaby is a practicing Muslim and, while growing up, developed a fascination towards the subjects of religion, philosophy, science, and astronomy.

While at Aubervilliers, Diaby was coached by David Giguère and Alain Mboma, the latter now serving as the manager of Red Star Paris.

[14] Towards the end of his development at Clairefontaine, Diaby departed Red Star to play domestic football with professional club Paris Saint-Germain, despite being a supporter of Marseille.

In his first season in the club's youth academy, he won the Division d'Honneur des 16 ans, the under-16 league title of the Bourgogne region.

[25][26] Unlike fellow youngsters Sagna and Kaboul who were quickly establishing themselves at their respective positions, Diaby only featured in five league matches during the first half of the season.

[27][28] In Europe, Diaby featured as a starter in the team's first round defeat to Bulgarian club Levski Sofia in the UEFA Cup.

[35] On 21 February, Diaby made his UEFA Champions League debut appearing as a substitute in the team's Round of 16 first leg victory over Spanish club Real Madrid.

[38] On 1 May, Diaby suffered a severe ankle fracture after being on the receiving end of a tackle, described by the media as "horrendous", from Sunderland defender Dan Smith.

[43] Following the surgeries, he underwent eight months of rehabilitation and made his return to first team action in the 2006–07 season in a League Cup match against Liverpool.

[44] On 25 February 2007, while participating in the 2007 Football League Cup Final against Chelsea, Diaby, while attempting to clear the ball out of the Arsenal defense, accidentally kicked rival defender John Terry in the face.

Unconscious, Terry was stretchered off and hospitalized, but recovered to return to the Millennium Stadium in Cardiff for the trophy presentation following Chelsea's 2–1 win.

He scored the first goal on 12 December in the team's final Champions League group stage match against Romanian club Steaua București.

On 29 March 2008, Diaby was sent off for the first time in his professional career in a league match against Bolton Wanderers for a studs-up tackle on defender Grétar Steinsson.

Wenger also stated that Diaby's tackle should not be compared to what had happened to teammate Eduardo da Silva a few weeks earlier.

[55] Wenger was, subsequently, criticized by the English media for flip-flopping on the subject due to providing differing statements when Arsenal players are on the receiving end of tackles and when they are the aggressors.

[citation needed] After serving his red card suspension, Diaby featured in only one match in the final two months of the season.

[66] The following month, Diaby assisted on a goal in the team's 3–2 comeback win over Belgian club Standard Liège in the Champions League.

[67] After alternating between the bench and starting lineup for the rest of September, in November, Diaby returned to the first eleven and responding by scoring the game-winning goal in a 3–1 win over Birmingham City.

The team went on to concede four unanswered goals while playing with ten men, which resulted in the club leaving St James' Park with only a point.

[82] On 11 May 2014, Diaby returned from injury as a substitute in a 2–0 win at Norwich City in Arsenal's final match of the 2013–14 Premier League season.

[86][87] Following continuing injury problems in the first half of the season,[88] he made his return on 18 March 2016, coming on as a substitute in Marseille's 5–2 home defeat to Rennes.

Due to repetitive injuries, he missed every qualifier for the 2007 UEFA European Under-21 Football Championship and made only one more appearance for the team, which occurred in a 1–1 draw in a friendly match with Armenia.

[100] On 15 March 2007, Diaby was called up to the senior team for the first time by coach Raymond Domenech for UEFA Euro 2008 qualifying match against Lithuania and a friendly against Austria.

The midfielder experienced several call ups to the team during the three years, but either withdrew from the squad due to injury or was not preferred by Domenech for a match.

Ahead of the competition, it was reported that Domenech was considering changing up the style of play in the team's 4–3–3 formation with Malouda possibly moving from the winger role into the midfield.

Following Malouda's relegation to the bench for insubordination, Diaby was inserted in his place and made his World Cup debut in the team's opening group stage match against Uruguay.

After over a year without an appearance at international level, Diaby returned to the national team in September 2012 under new manager Didier Deschamps.

[117] During his early years with Auxerre, he was often used as an attacking midfielder or a support striker due to his technical ability, close control, and dexterity to dribble past opponents or slip passes to teammates.

[6][118][119] While the two are similar in appearance, Diaby has admitted that there are huge differences, stating, "I think maybe I am more attack-minded, a more technical player," and, "Vieira is much more aggressive.