The Defence of India Act 1915, also known as the Defence of India Regulations Act, was an Emergency Criminal Law instituted by the Governor General of India in the year 1915. The British Government enacted it with the objective of restricting the revolutionary and nationalist activities and endeavours and German supported threats, during the aftermath of World War I. The arrival of World War I served as a cause for the intensification of the forces of the nation. The British administration aimed to curb the armed revolution movement by the political terrorists. In the year 1908, the British authorities passed the Newspapers (Incitement to Offences) Act and the Explosives Substances Act, and eventually the Indian Press Act, the Prevention of Seditious Meetings Act and the Criminal Tribes Act. The Defence of India Act was later applied during the First Lahore Conspiracy trial in the aftermath of the failed Ghadar Conspiracy of 1915. After the culmination of World War I, the Defence of India Act 1915 formed the basis of the Rowlatt Act.

The Defence of India (Criminal Law Amendment) Act, 1915 (No.4) law was equivalent to the British Defence of the Realm Acts. It was passed though all the phases in the Legislative council on 18 March 1915. The law was instituted as a provisional legislation in effect for the duration of the First World War and for a period of 6 months after it.

The Defence of India Act 1915 provided the authority to the Governor General in Council to construct rules with the objective of securing the public safety and the defence of British Empire in India. It also defined the duties and powers of public servants and other individuals for the advancement of that purpose. Contravention, violation and breach of the law was punishable by a fine, or imprisonment of up to 7 years, or both, or, if the aim of the person was to assist the enemies of the British Government or commence war against the British Crown, punishments could be more severe and stringent, including death sentence.

Sections of the law were implemented in certain provinces by notification of the Governor General in council and were incorporated in the act for Bengal and Punjab. These sections authorized the local administration to establish special courts that comprised of 3 commissioners with authority to try for particular offences and without any right to appeal.