Ficino was born at Figline Valdarno. His father Diotifeci d'Agnolo was a physician under the patronage of Cosimo de' Medici, who took the young man into his household and became the lifelong patron of Marsilio, who was made tutor to his grandson, Lorenzo de' Medici. Giovanni Pico della Mirandola, the Italian humanist philosopher and scholar was another of his students.
During the sessions at Florence of the Council of Ferrara-Florence in 1438–1445, during the failed attempts to heal the schism of the Eastern (Orthodox) and Western (Catholic) churches, Cosimo de' Medici and his intellectual circle had made acquaintance with the Neoplatonic philosopher George Gemistos Plethon, whose discourses upon Plato and the Alexandrian mystics so fascinated the learned society of Florence that they named him the second Plato. In 1459 John Argyropoulos was lecturing on Greek language and literature at Florence, and Ficino became his pupil.
When Cosimo decided to refound Plato's Academy at Florence he chose Ficino as its head. In 1462, Cosimo supplied Ficino with Greek manuscripts of Plato's work, whereupon Ficino started translating the entire corpus to Latin (draft translation of the dialogues finished 1468–9; published 1484). Ficino also produced a translation of a collection of Hellenistic Greek documents found by
Leonardo da Pistoia later called Hermetica, and the writings of many of the Neoplatonists, including Porphyry, Iamblichus and Plotinus.
Among his many students was Francesco Cattani da Diacceto, who was considered by Ficino to be his successor as the head of the Florentine Platonic Academy. Diacceto's student, Giovanni di Bardo Corsi, produced a short biography of Ficino in 1506.
A physician and a vegetarian, Ficino became a priest in 1473.