WASHINGTON—An insider of the secretive world of high-frequency trading is set to attack that industry Thursday on Capitol Hill, giving lawmakers a potential road map to address practices that critics say can put ordinary investors at a disadvantage and the financial system at risk.

Since rapid-fire trading firms now provide many of the buy and sell orders that support the market, investors are at the mercy of automated systems that can run amok during volatile times, according to Dave Lauer, who last year quit his job as a...