Chinese President Xi Jinping issued a full-throated defense of international trade and economic integration before a packed hall here, as doubts about the merits of globalization mount in the U.S. and elsewhere in the West.

“No one will emerge as a winner in a trade war,” Mr. Xi, the leader of the world’s second-biggest economy, said in an hourlong speech on Tuesday to members of the world elite gathered for the annual World Economic Forum. “Pursuing protectionism is just like locking one’s self in a dark room. Wind and rain...