Westerveld was in South Africa in July to meet with the Ajax technical team and management. He was recommended to the Ajax management as a possible replacement for Hans Vonk who retired at the end of last season.
Sander started his professional career at FC Twente and has since played for Liverpool, Everton, Real Sociedad and Sparta Rotterdam. Last season he played for Monza in Italy making 54 appearances.
Westerveld arrives on Saturday to start his new venture with Ajax Cape Town.