The Amsterdam club decided against renewing the contract of Heitinga, 39, after he failed to guide Ajax to qualification for the Champions League for the first time since 2009.
However, he had only taken charge in January and still lifted the Dutch giants from fifth to third in the Eredivisie table having stepped up from the club’s youth academy.
Heitinga is joined at West Ham by fellow new first-team assistant coaches Henry Newman and Mark Robson.
Robson has been promoted from his role in the Hammers youth system while Newman has worked at West Ham for four years as an analyst. He had previously taken interim charge of then-League Two side Barnet in 2016-17 before being involved in a failed takeover bid for struggling Bury four years ago.
“John is someone I have known for a long time,” Moyes said of Heitinga, who spent four years at Everton during his playing career.
“He has gained some very good experience since beginning his coaching career in the Ajax Academy and working his way up to their first-team. Mark and Henry are both already familiar to everyone here at the club and have deserved the opportunity to step up within our structure.”