IEX Group, the upstart trading venue that says it protects investors from predatory high-speed-trading tactics, has hired a top former regulator to help with its efforts to transform into a stock exchange.

IEX hired John Ramsay, former acting head of the Securities and Exchange Commission's Trading and Markets division, which oversees major market players such as broker-dealers and stock exchanges. Ramsay, who left the SEC in March, marks the biggest new hire for IEX, which was featured in Michael Lewis's "Flash Boys" for its efforts to create a market that stymies high-frequency-trading firms.