The amended bill bans 40 kinds of rifles including the AR15, requires fingerprinting and licensing of all purchasers of new guns and broadens the law prohibiting firearms purchases by anyone who is involuntarily committed because of mental illness.
The bill was a major component of O'Malley's legislative package announced at the beginning of the 90-day session.
The House of Delegates debated the bill for nearly 10 hours over two days.
The amended bill will return to the Senate. The bill could go to a conference committee if the Senate does not accept the changes made by the House.
Both the House and Senate must agree on the same bill before midnight Monday.