The Second Federal Republic of Mexico refers to the period of Mexican history involving a second attempt to establish a federal government in Mexico after the fall of the unitary Centralist Republic of Mexico in 1846 at the start of the Mexican-American War. It would last up until the Second French Intervention in Mexico led to the proclamation of the Second Mexican Empire in 1863.

The Centralist Republic of Mexico, or in the anglophone scholarship, the Central Republic, officially the Mexican Republic, was a unitary political regime established in Mexico on 23 October 1835, under a new constitution known as the Siete Leyes after conservatives repealed the federalist Constitution of 1824 and ended the First Mexican Republic. It would ultimately last until 1846, when the Constitution of 1824 was restored at the beginning of the Mexican-American War.