After the start of World War I, the French managers of the bank left Mexico. After 10 years, Agustín Legorreta Ramírez who served as acting president managed to revive the bank. Following its reorganization, the bank collaborated with Banco de Mexico and US government officials. By 1937, 36 out of 50 bank branches in Mexico were owned by Banamex.

Banamex gradually introduced several financial product innovations to the Mexican market including the first credit cards