Born in Lisbon on June 6th, 1502. Son of King Manuel and D. Maria, daughter of the Spanish Catholic Kings. Rose to the throne at the age of 19 after his father´s death in 1521. Married with Catherine of Austria, sister of Charles V, in 1525.
Becomes Governor and Keeper of the Order of Christ when crowned King of Portugal and is responsible in 1528 for a profound reform in the Order - constricting the religious friars of the Order to observance of a life of enclosure. The leading figure of this reform will be Friar António da Silva - religious man of the Jerónimos of Guadalupe - and confessor of the King.
This reform will pave the way to the grandiose Rebirth convent, implemented to the west, beyond the walls of the castle, around the nave, where his father extended the Templar church.
The Holy See gives King John III the right for Portuguese Kings to perpetually become masters of the Order of Christ. As a result, King Philip II of Spain, heir to the Portuguese throne, becomes the master of the Order of Christ after Portugal loses its independence in 1580.
The King was involved in the Order of Christ in the person of its reformer and high-priest, Friar Anthony of Lisbon, in the actions of the Holy Office Court and thus the Tomar Convent being a part of the proceedings and execution of sentences.
The patronate of the Order of Christ Overseas was extinguished and the Funchal Diocese was created to run the spiritual of the churches that the order had in Madeira, Azores, Africa, Asia and Brazil.
A monarch interested in the Renaissance movement while at the same time his religious conduct was driven by the spirit of the Counter Reform from Rome. Even though the King had inherited a vast empire from his father, the kingdom was faced with serious economical and social strife. In his court lived men such as Garcia de Resende, Damião de Góis and Gil Vicente. There are records of the representation of the "Farsa de Inês Pereira" play in the Convent of Christ in 1523.
Reigned for 36 years and died in Lisbon on June 11th of 1557 and is buried at the Jerónimos Monastery.