The Founders' Chapel is located to the right of the main façade. It was not included in the monastery's original plan and owes its existence to King John I's decision to build a family pantheon. Construction was completed around 1433/34. It is a space rich in historical and artistic significance. Originally square in plan, it transforms into an octagon in the center, covered by a complex star-shaped vault that becomes a veritable canopy glorifying King John I and Queen Philippa of Lancaster, buried in a large tomb. On the lid of this, the largest 15th-century Gothic arch in Portugal, the two kings are depicted reclining, holding hands, covered by canopies bearing their coats of arms.
On the rear wall, on the south side, are the tombs of the children of these kings, from the second quarter of the 15th century, the "Illustrious Generation," as Camões called them. From right to left: Tomb of the Infante and Regent Dom Pedro and his wife Isabel de Urgel, Duchess of Coimbra; of Henry the Navigator and Master of the Order of Christ (with reclining statue); of Infante Dom João, Master of the Order of Santiago, and his wife Isabel; and of King Ferdinand, Master of the Order of Aviz, who died a saint while imprisoned in Fez.
The three caskets commissioned by King Charles I date from the early 20th century and are located on the west side of the chapel. Buried here, from left to right, are: King Afonso V, grandson of John I; King John II, son of Afonso V; and finally, Crown Prince Afonso, son of John II, who died prematurely in 1491 in a riding accident in the Santarém region.