The midfielder puts pen to paper on a four-year deal with the Eredivisie giants, in what is increasingly becoming a busy summer in South Holland
Ronald Koeman's side previously tried to land the 25-year-old last summer, as both clubs failed to strike an accord in negotiations, but the former Netherlands defender has finally got his man.
Immers returned from his holiday in Turkey and attended a medical examination at De Stadionclub, before penning a four-year contract and being allocated the No.10 jersey for next season.
However, the arrival of Immers, who scored 33 goals in 164 appears for ADO, may cast doubt over the future of star Otman Bakkal, who spent the past campaign on loan from PSV.
Technical director Martin van Geel had revealed in the past that he would prefer the Dutchman to stay, having played a key role in the side finishing an impressive second place in the 2011-12 Eredivisie.
Nonetheless, Immers becomes Feyenoord's fifth signing of the close season, along with Daryl Janmaat, Ruud Vormer, John Goosens and Mitchell te Vrede.