Sáenz Garza served as Secretary of Foreign Affairs during Calles' time as President. During his tenure, he continuously defended the Calles Administration's decision to cut oil to the United States when US Secretary of State Frank Kellog tried to bargain for a deal. He soon became Governor of Nuevo León and maintained close ties with Calles; as Governor, he even sat with Calles when he questioned the assassin of President-elect Alvaro Obregon in 1928. It was also announced that Calles had plans to nominate him as the Chairman of the National Revolutionary Party.PresidentPascual Ortiz Rubio appointed him Secretary of Public Education on February 1930. By 1934, Saenz had been dubbed as the "Shadow of Calles" and was named Governor of Mexico's Federal District by Mexican President Lázaro Cárdenas. Cardenas and the Mexican Congress, however, soon turned on both Calles and Saenz and condemned their continued persecution against Catholics in the country.
After leaving office in 1935, Saenz established a sugar corporation and quickly revolutionized sugar production in the country. He was also known as the "king of Mexican sugar", founding a dynasty which survives until this date, led by his son Aaron Saenz Couret and grandson Aaron Saenz Hirschfeld, at the head of the leading sugar company in Mexico. At one point, he held a virtual monopoly of Mexico's sugar industry. His monopoly, however, was brought down during the administration of Mexican president Adolfo Ruiz Cortines by 1953. Saenz was married to Margarita Couret, with whom he had eight sons. For some time they all managed varied branches of the family's businesses, most of which have ceased to exist or passed into others' ownership. Most notable among these were: