The Karnataka government notified Friday the anti-conversion law after it received Governor Thaawarchand Gehlot's assent.
The Karnataka Protection of Right to Freedom of Religion Act, whose Bill was passed in the state legislature earlier this month, seeks to prohibit "unlawful conversion from one religion to another by misrepresentation, force, undue influence, coercion, allurement or by any fraudulent means".
Gehlot gave his assent on September 28, according to the notification.
The law will come into effect retrospectively from May 17, 2022, when the government had promulgated an ordinance.
The law has caused anxiety, especially among a section of Christians.
The Opposition has argued that the law is "unconstitutional". In defence, the ruling BJP said the law would curb "forced" religious conversions.