The French left-back has penned a four-year deal with Los Che to become their sixth summer signing
The French left-back will sign a four-year contract after the sides agreed a fee believed to be in the region of €6 million (£4.7m).
Speaking to the club's official website, Los Che sporting director Braulio Vazquez stated his delight with the club's newest summer addition.
“Aly is a player with vast international experience that belies his youth. He has played for the French national team and has participated in high-level games in competitions such as the Champions League.
"Cissokho is physically powerful, very strong defensively and someone who will increase the competitiveness of of the team - especially on the left side. With him and Mathieu we have the position extremely well covered."
With Andres Guardado, Sergio Canales, Fernando Gago, Joao Pereira and Jonathan Vieira already having joined the ranks at the Mestalla, Vazquez is confident of his side's chances in the 2012/13 campaign.
"This latest signing completes a very strong squad in all aspects, which excites us immensely. We have a lot of quality in every position and can approach the current season with plenty of optimism -both that the fans will enjoy watching us play and that we can achieve great things in this campaign."
Mauricio Pellegrino's side enjoyed a respectable 1-1 draw away to Real Madrid on the first matchday of the new season, and will entertain Guardado's former club Deportivo La Coruna on Sunday.