A new competitor is set to enter the stock-exchange business, planning to launch a marketplace even as some on Wall Street question whether another trading venue is necessary.

Miami International Holdings, which has roughly tripled its share of the stock-options market over the past five years, is preparing to launch its MIAX Equities Exchange toward the end of this year or in early 2020, Chief Executive Officer Thomas Gallagher said in an interview. The plan, which was floated in 2011, is subject to regulatory approval.