Finmeccanica's Anglo-Italian subsidiary AgustaWestland will form a joint venture with Russian Helicopters, a unit of public holding company Rostec, to assemble the AW189 helicopters designed for offshore operations.
Rosneft "will be the first client" for these aircraft and plans to buy 160 of them between now and 2025, the group said in a statement.
The deal signed on Monday comes as sanctions imposed by the United States and the European Union have slowed or frozen many joint projects between Western multinational companies and Russia.
Both Rosneft and Rostec, two powerful public groups headed by close allies of President Vladimir Putin, have been targeted by the Western sanctions.
The AW189 helicopter, especially adapted for offshore operations including search and rescue missions, can carry 16 passengers and has a flying range of 600 nautical miles (1,111 kilometres).