The 32-year-old arrives as a free agent, having left Crystal Palace at the end of last season. The Senegalese international spent four years at the South London club following a four-year spell at West Ham United.
Capable of playing at centre-back and in midfield, Kouyaté began his career in Belgium with RWDM Brussels in 2007 before moving to Anderlecht where he spent six years and then making a £7m move to West Ham.
Having made 82 appearances for Senegal, including winning the 2021 Africa Cup of Nations, Kouyaté is a versatile addition to Steve Cooper’s squad with a wealth of international and Premier League experience.
Swiss international Remo Freuler is also believed to be set to join on a three-year contract from Atalanta.
Cooper’s team face their first home game of the Premier League season this afternoon as they welcome West Ham United to the City Ground.