Foxtons, which returned to the stock market last year, said Brown was stepping down for “personal reasons”, sending shares tumbling 6.6 per cent yesterday.
It comes after he took a period of compassionate leave earlier this year.
Brown, who joined Foxtons in 2002, took over as chief executive in 2007 when founder Jon Hunt sold the company to private equity firm BC Partners.
He led its successful float in September and is widely credited for turning around the indebted business after the financial crisis.
Brown will hand over the reins to chief operating officer Nic Budden in July but he will stay on the board as a non-executive director.