Extreme Risk Protection Order and Violence Prevention Act of 2018 This bill amends the Omnibus Crime Control and Safe Streets Act of 1968 to establish a new grant program to help states and Indian tribes carry out laws that authorize and establish procedures for a family or household member, or law enforcement officer, to petition a court for an extreme risk protection order with respect to an individual who poses a significant danger to themselves or others. An extreme risk protection order is a state or tribal court order that prohibits an individual from purchasing, possessing, receiving, or having control or custody of a firearm. Additionally, the bill amends the federal criminal code to expand the categories of prohibited persons (i.e., persons barred from receiving or possessing a firearm or ammunition) to include persons who are subject to a court order that restrains them from possessing and purchasing a firearm.