Born in Paris, France, N'Diaye began his career with US Vandœuvre in Vandœuvre-lès-Nancy. At the age of 14, he moved across the arrondissement to join the biggest club in the region, AS Nancy. Upon arrival, Alfred endured early struggles, but quickly gained noticed following his second season at the academy. In 2006, he signed his first professional contract.
Nancy
N'Diaye made his debut in the squad during the 2007–08 season in the Coupe de la Ligue, at the age of 17, coming on as a halftime substitute for Frédéric Biancalani in a 0–3 loss to Lens. That was his only appearance that season as he would be relegated back to the reserves helping a young Nancy reserve squad barely avoid relegation. Following the season, N'Diaye earned promotion to the senior squad for the 2008–09 season. He was assigned the number 29 shirt and made his league debut in the opening match of the season against Lille appearing as a substitute in a 0–0 draw. Two months later, he earned his first league start in a 1–1 draw against Paris Saint-Germain. His positive play earned him regular starts in the squad, including playing the full 90 minutes in the club's 3–0 upset victory over Olympique de Marseille at the Stade Vélodrome and playing, on two occasions, 120 minutes of football in cup play against Grenoble in the Coupe de la Ligue and SO Romorantin in the Coupe de France. In total, he made 27 appearances and collected 7 yellow cards.
On 1 July 2011, Nancy confirmed on its website that the club had reached an agreement with Turkish club Bursaspor for the transfer of N'Diaye. The deal was finalised on 3 July for a reported fee of €2 million.
On 9 January 2013, it was announced that Sunderland had completed the signing of N'Diaye for an undisclosed fee. He was given the number 4 shirt. On 12 January 2013, N'Diaye made his Sunderland debut at the Stadium of Light in a match which they won 3–0 against West Ham United. He came on as a substitute for Adam Johnson and almost scored with his first touch in English Football as his shot went just wide. His full debut for Sunderland came against Wigan away, in which he produced a "wonderful" assist for Steven Fletcher to score and put them in front.
Eskişehirspor (loan)
On 28 July 2013 it was announced N'Diaye would join Turkish club Eskişehirspor on a season-long loan. On 28 January 2014, Eskişehirspor announced that N'Diaye's loan had been terminated by the club.
Betis
On 30 January 2014, N'Diaye joined Spanish side Real Betis on loan for the remainder of the 2013–14 campaign. He appeared in 16 matches, as the Andalusians were relegated. On 22 August 2014, free agent N'Diaye signed a five-year deal with the Béticos.
Villarreal
On 8 July 2016, N'Diaye signed a five-year contract with Villarreal CF also in the main category.
On 31 January 2017, N'Diaye moved on loan to Hull City for the remainder of the 2016–17 Premier League season. N'Diaye made his debut and scored the first goal in a home 2–0 victory over Liverpool. Impressing during his 15 games at the club in a short spell, despite being unable to keep Hull in the Premier League.
On 31 August 2017, the transfer deadline day of the 2017/18 summer transfer window, N'Diaye completed a last-gasp loan deal to English Championship club Wolverhampton Wanderers. He made his debut for the club on 9 September 2017, coming on as a substitute in a 1–0 win against Millwall. He scored his first goal for the club on 23 September 2017 in a 2–1 win against Barnsley after coming on as a substitute. He played 36 games for Wolverhampton Wanderers in all competitions, as he helped the club win the EFL Championship title and gain promotion to the Premier League.
On 30 August 2019, N'Diaye moved to Saudi club Al-Shabab FC on a three-year contract.
International career
Having played through the France national youth football teams, he decided to play for Senegalnational football team and played his first senior international match in 2013. In May 2018 he was named in Senegal's 23-man squad for the 2018 FIFA World Cup in Russia. with N'Diaye playing for Senegal in 2 matches during the tournament, against Poland and Japan.
