Niccolò III d'Este (9 November 1383 – 26 December 1441) was Marquess of Ferrara from 1393 until his death. He was also a condottiero.

Born in Ferrara on 9 November 1383, Niccolo was the son of Alberto d'Este and Isotta Albaresani. He inherited the rule of the city in 1393 when only 10 years old. As a minor he was guided by a Regency Council supported by the Republics of Venice, Florence and Bologna.

Niccolò's uncle Azzo X d'Este, a descendant of Obizzo II d'Este, contested Niccolò's right to rule in Ferrara due to his illegitimate birth, even though Niccolò had been legitimated by his father. In 1395 Azzo invaded Ferrara with a mercenary army, but was defeated and captured in the Battle of Portomaggiore by the troops of the Regency Council.

In 1397 Niccolò married Gigliola da Carrara, daughter of Francesco II da Carrara, lord of Padua.

In 1403 he joined the league formed against Gian Maria Visconti, Duke of Milan, being appointed Captain General of the Papal Army by Pope Boniface IX. In 1405 he ceded the ancestral family lands near Este to Venice.

In 1410, the fencing master Fiore dei Liberi dedicated his treatise Fior di Battaglia to him. In 1413 he made a pilgrimage to the Holy Land. In 1418 he remarried, to Parisina Malatesta, daughter of Andrea Malatesta. Two years later, fearing the ambitions of Filippo Maria Visconti, he ceded Parma to him.

In 1425 Niccolò had both his wife Parisina and his illegitimate son Ugo executed on charges of adultery, and also decreed that all women within his domains found to be guilty of adultery were to be put to death. He had to rescind this order once it was determined that this action would depopulate Ferrara. In that year he was again commander-in-chief of the anti-Visconti league. In 1429, he named his illegitimate son Borso as heir of the Marquisate.

The role of Niccolò as a prestigious leader in Italy was confirmed when his city was chosen as the seat of the Council of Ferrara in 1438.