Fox is to be replaced by Jim Mullen, previously chief executive of Ladbroke Coral. Other previous roles include director of product management and director of digital strategy at News UK.
Nick Prettejohn, chairman of Reach said: "I would like to thank Simon for the great job he has done over the past seven years. As the first half results demonstrate, he leaves Reach in very good health, with a strong balance sheet and real progress in developing the business for the future. We have an excellent successor in Jim and I am pleased to have a seamless transition."
Simon Fox said: "There is never an ideal time to leave an organisation, but if there were it would be now. The integration of the Express and Star national newspapers has been successfully completed, digital growth is accelerating and our trading and cash position are strong.
“I am proud of what has been achieved and will provide Jim with whatever support is required to ensure a smooth handover."
Jim Mullen said: "I am delighted to be joining Reach at such an exciting time and look forward to building upon its digital transformation."
Earlier this month, reported The Guardian, Reach confirmed it was in discussions to acquire some of the titles owned by JPI Media, which publishes the i as well as local and regional newspapers including the Scotsman and the Yorkshire Post.