Once able to rely on larger-than-life finance ministers, the region’s business leaders now need to make the public case for free markets via retail politics.

With its clean energy matrix, the region could capitalize on the green transition—if leaders in Mexico and Brazil get with the program.

Over the past decade, illiberal populist leaders from across the political spectrum have won elections and taken power in many of the world’s biggest democracies, from the United States to India, the…