NEW DELHI—India will buy 113 fighter jets and helicopters from Russia in a major boost to the longstanding defense ties between the two countries.

Under agreements signed Monday, India will acquire 42 Sukhoi Su-30 MKI fighter jets that will be produced under license by state-run Hindustan Aeronautics Ltd. It will also purchase 71 Mi-17 V-5 helicopters that will be produced by Russian Helicopters.

The...