The agreement, driven by a search for new partnerships to shield their markets from a volatile America, will deepen ties between the 27-nation E.U. — a trading power that is traditionally Washington’s closest partner — and India, among the world’s fastest-growing major economies.

“We have concluded the mother of all deals,” European Commission President Ursula von der Leyen said. “We have created a free-trade zone of 2 billion people, with both sides set to benefit. This is only the beginning.”