MEXICO CITY—A prominent billionaire ally of Mexico’s president has financial ties to companies that profited from a deal at the center of a burgeoning corruption scandal in the country.

Ricardo Salinas Pliego, who heads a business empire with assets in banking, broadcasting and retail, is linked to Europe-based entities that held large shares of Grupo Fertinal, according to people familiar with the matter and internal corporate documents reviewed by The Wall Street Journal.

Fertinal...