The FBI says Sandy Winick pleaded guilty on Friday and faces a maximum sentence of 20 years in prison.
An FBI news release says Winick, 57, was the leader of a multimillion-dollar scheme that used call centres around the world to defraud victims.
The agency says the scheme involved collecting advance fees from investors for the purchase of penny stocks but no services were provided.
The FBI says victims were defrauded of more than $5 million.
Winick was extradited from Thailand to face the American charges.
The FBI says the Ontario man is the seventh person to plead guilty in the case so far.
Winick has also had troubles with the authorities in Canada.
The Ontario Securities Commission ordered Winick and another man to pay more than $1 million in 2013 for the illegal distribution and unregistered trading of securities.