The RFU announced on Wednesday afternoon that Ritchie, 63, had informed its board of directors, management and staff of his decision.
Yorkshire-born Ritchie joined the RFU in February 2012, and has overseen England hosting the World Cup in 2015 and the England team winning back to back-to-back RBS Six Nations Championships in 2016 and 2017.
Ritchie also negotiated the Professional Game Agreement with PRL this year, worth over £200m to Premiership club rugby in England over the next eight years.
He said: “It has been an honour and a privilege to lead the RFU. I’m proud to have been part of the rugby family, working with so many talented, passionate and committed teams at every level of the game and of the Union.
“Rugby is a special sport, and one which is very hard to leave, but after a 40-year career and seven CEO roles, I will retire at the end of the summer with a lifetime of memories, many of which have rugby at heart.
“I would like to thank Andy Cosslett, the board, and everyone at the RFU for their support.”
The RFU says it will now begin the process of recruiting Ritchie’s successor and expects an appointment to be made by the end of the summer.
RFU chairman Cosslett said: “Ian has been an outstanding CEO.
“He has led the RFU through a period of sustained growth and success, built a terrific management team of executives and coaches, and kept the values of rugby at the heart of his leadership style.
“On behalf of the board of the RFU, I would like to thank him for his significant and lasting contribution to English rugby.”