Historians debate whether Tomás de Mercado was born in Seville or Mexico, and he lived between 1525 and 1575. He entered the Dominican order as a young man within the walls of Mexico City before returning to Europe.
Tomás de Mercado collaborated closely with Martín de Azpilcueta to establish a distinct economic tradition known as Iberian monetarism. Their partnership formed part of the broader intellectual movement called Late Scholasticism or the School of Salamanca.
The resulting book appeared in 1571 under the title Summa de Tratos y Contratos after Sevillian merchants requested an expanded edition of his earlier 1569 publication titled De los tratos de India y tratantes en ellas. This manual became his most famous work and remains central to understanding his economic theories today.
Tomás de Mercado strongly supported the fixed price set by the government known as tasa del trigo even if it meant producers sold at a loss. He viewed these price control policies as a divine obligation made to the prince responsible for the kingdom's peace.
A chapter dedicated to the African slave trade revealed Tomás de Mercado highly critical stance on actual trading practices while regarding it acceptable for Europeans to buy slaves enslaved by Africans themselves. He also accepted the enslavement of captives taken in war or those sentenced for crimes.