The Appointments Committee of the Cabinet has approved extension of his tenure for one year with effect from June 4, an order issued by the Department of Personnel and Training (DoPT) said.
Reddy, a distinguished scientist of the Defence Research and Development Organisation (DRDO), was in June 2015 appointed to the post for a fixed two-year term.
Finance Minister Arun Jaitley is looking after the charge of the defence ministry, following the appointment of Manohar Parrikar as the Goa chief minister.
Reddy is an eminent missile scientist and has made pioneering contributions to navigation and avionics technologies.
Earlier, the DRDO chief used to be the adviser to the defence minister.