Pietro Usimbardi (9 January 1539, Colle di Val d'Elsa – 28 May 1611, Arezzo) was an Italian Catholic bishop who also served as a secretary for Grand Duchy of Tuscany.

Pietro was the eldest of five sons: Lorenzo (1547–1636) followed his brother's path into politics; Usimbardo (1552–1612) became the first bishop of the diocese of Colle; Claudio (1556–1638) and Fulvio (1559–1627) also pursued successful careers.

All the brothers received a strong education in law and theology, which prepared them for their future roles in public service.

The following year, he was appointed parish priest of the Church of Santa Maria a Limite and granted the office of propositura in Cigoli.

Pietro Usimbardi personally funded the church's restoration and, in 1585, donated it along with its surrounding lands to the Order of Saint Francis of Paola.

This secretariat included Antonio Serguidi (Francesco's minister, whose power was significantly diminished), Belisario Vinta (a key figure during Ferdinando I's reign), and Pietro Usimbardi.

Additionally, he oversaw the general treasury, the university and College of Pisa, matters of grace and justice, and ceremonial functions at court.

In the late 1580s, it seemed likely that Usimbardi would be elevated to the rank of cardinal, but the death of Sixtus V in August 1590 put an end to this possibility.

This was because Usimbardi did not interfere in the Grand Duke's affairs unless specifically asked or practically compelled to do so, and he only offered advice when requested.

In 1593, Pietro's "particular experience and knowledge of the Roman court"[4] led him to continue advising Ferdinando on various matters, including encouraging him to pursue the reclamation of the Val di Chiana.

[2] Although he obtained the episcopal office through the recommendation of the Grand Duke to Pope Sixtus V, Pietro's work in Arezzo was regarded as one of the most significant in the diocese's history.

Its decoration was a prestigious project, entrusted to renowned artists like Ludovico Cigoli, Matteo Rosselli, Cristofano Allori, and Iacopo da Empoli.

In 1597, Pietro presided over a synod that embraced the principles and decrees of the Council of Trent, later published in his principal work: Constitutiones et decreta published in the Synodo diocoesana Arretina, quam Petrus Usimbardius episcopus Arretij habuit anno Domini MDXCVII, printed in Florence by B. Sermartelli in 1598.