The 50-year-old has announced he will not extend his stay with the club beyond the summer early enough to allow the Eredivisie side time to find a successor
The 50-year-old, who replaced Mario Been in 2011, admits he has relished his three-year spell with the Rotterdam outfit but says he has made the announcement now in order to allow the club time to find a successor.
"I've worked well working closely with the players, the staff and all the others here at the club. I've been enjoying myself here from day one. The decision not to sign [a new deal] is one that I've made purely by feeling," he told the club's official website.
"Feyenoord deserve to have certainty over their future. I'm working with the group to reach a beautiful end result and bring three fantastic years together to a close."
Club technical director Marco van Geel confessed he would have preferred Koeman to extend his deal but was quick to pay tribute to his work over the past three seasons.
"We would have liked to have gone another year with Ronald, but it is convenient to have clarity from the off - now we have plenty of time to find a successor," he said.
"It is not surprising that a trainer wants to look further ahead after a fantastic performance over three years. In that sense, I am not really surprised or amazed by his decision."
Former Netherlands international Koeman became the first man to enjoy spells as both player and coach of traditional Eredivisie powerhouses Ajax, PSV and Feyenoord when he arrived at the club in 2011.
Feyenoord currently sit fourth in the table, six points adrift of leaders Ajax.