About 40,000 square miles off the tip of South America would be off limits to fishing, energy development, and other activities under a bill Argentina’s Senate approved creating two marine protected areas.

The bill—part of a deal struck by Argentina’s major political forces on a number of legal measures—passed the Senate Dec. 12 in a 59-1 vote, a week after being approved in the lower house.

An official with the environment secretariat, speaking on condition of...