Born in Bamako, Mali, Keita finished his football formation in France with Olympique de Marseille, joining the club at the age of 17.

Keita made his Ligue 1 debut for L'OM on 19 September 1999 in a 1–0 home win against Troyes AC, adding three games in the season's UEFA Champions League.

He appeared slightly less due to injury in the following season, which ended in immediate relegation, but brought the conquest of the Coupe de France, the club's first-ever; he played the full 90 minutes in the final against SC Bastia.

[13][14] The following week he added another, in a 1–1 home draw to Getafe;[15] he finished his first season at the Camp Nou with 46 official appearances as Barça won the treble, and played 20 minutes in the Champions League final, taking the place of Thierry Henry in the 2–0 triumph against Manchester United.

[16] On 25 October 2009, Keita scored his first career hat-trick, in a 6–1 home win against Real Zaragoza,[17] and contributed with 29 games – 23 starts – as Barcelona renewed its domestic supremacy.

The following day, he signed a two-and-a-half-year deal with Chinese Super League side Dalian Aerbin, being reportedly paid €14 million per year.

[22] On 13 March, midway through the first half of an away fixture against PFC Ludogorets Razgrad for the UEFA Europa League, he was sent off for a challenge on Roman Bezjak that resulted in a penalty kick, but his team eventually won it 3–0[23] and 4–0 on aggregate.

[26] He made his competitive debut in the opening day of the season, against ACF Fiorentina (2–0 win),[27] and scored his first goal on 9 November to help defeat Torino F.C.

[30] Keita helped Mali's under-20s finish third at the 1999 FIFA World Youth Championship in Nigeria, scoring the only goal[31] in the last match against Uruguay, and being named the tournament's best player.