The 24-year-old will move to the Spanish club on a four-year deal, providing he passes a medical.
Valencia's sporting director Braulio Vazquez told the club's official website: "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.
"This latest signing completes a very strong squad in all aspects, which excites us immensely."
Cissokho joined Lyon from Porto in 2009.