Nikhil Gupta, 54, pleaded guilty to murder-for-hire, conspiracy to commit murder-for-hire and conspiracy to commit money laundering, which carry a maximum combined sentence of 40 years in prison, the spokesperson said.
Gupta entered his plea before US Magistrate Judge Sarah Netburn in Manhattan federal court.
Lawyers for Gupta were not immediately available for comment.
Gupta has been jailed in Brooklyn since his June 2024 extradition to the United States from the Czech Republic, where he had been arrested a year earlier.
He had pleaded not guilty immediately after his extradition.
US prosecutors accused Gupta of plotting with an Indian government official to kill Gurpatwant Singh Pannun, a US resident and dual US-Canadian citizen who advocated for a sovereign Sikh state in northern India.
India's government has dissociated itself from any plot against Pannun, saying it was against government policy.
The discovery of alleged assassination plots against Sikh separatists in the United States and Canada has tested relations with India, which has also denied involvement in such plots.