The 30-year-old player is a member of the Egyptian Premier League club Al Ahly but is going to leave the team.
Tau is regarded as one of the best wingers in Africa.
He started his playing career in the South African team Mamelodi Sundowns in 2013 and has also played at the English Premier League side Brighton & Hove Albion and Belgian teams Union SG, Club Brugge and Anderlecht.
Esteghlal head coach Pitso Mosimane has previously worked with the player in Al Ahly.
Kaizer Chiefs is also going to sign the player.