Consecrated cathedral in 393 by Sant'Ambrosio, it was dedicated to San Lorenzo Martire. For three hundred years it was the city's cathedral before the official seat of the bishop was transferred to Santa Reparata. In 1418 the Medici Family decided to adopt it as "their" church. Filippo Brunelleschi, the leading Renaissance architect of the first half of the fifteenth century, was commissioned the task of renovating the building, but the building, with alterations, was not completed until after his death. Following his death, the church was finished by Antonio Manetti in 1461.
The church is part of a larger monastic complex that contains other important architectural works: the Old Sacristy by Brunelleschi, commissioned by Giovanni di Bicci de'Medici as his private chapel, dedicated to Saint John the Evangelist; the Laurentian Library by Michelangelo; the New Sacristy based on Michelangelo's designs; and the Medici Chapels by Matteo Nigetti; the cloisters which were expanded and restructured by Michelangelo. The interior of the church is divided into three aisles by arched colonnades that are matched by side chapels. The ceilings of the side aisles are vaulted, while the ceiling of the central nave is carved wood.