| Luigi Braschi Onesti | |
| Spouse: | Constanza Falconieri |
| Noble Family: | Braschi |
| Father: | Girolamo Onesti |
| Mother: | Giulia Braschi dei Bandi |
| Birth Date: | 1746 |
| Birth Place: | Cesena, Papal States (now Italy) |
| Death Place: | Rome, Papal States (now Italy) |
| Religion: | Roman Catholicism |
Luigi Braschi Onesti (1745– 9 February 1816), duca di Nemi, was a nephew of Pope Pius VI, who granted him his dukedom.
Luigi's mother Giulia Braschi was Pius's sister, and his father was count Girolamo Onesti. His younger brother was Romoaldo Braschi-Onesti, Cardinal and Camerlengo.
On Luigi's marriage to the richest lady of the Falconieri family, he was granted permission by Pius to build Palazzo Braschi off Piazza Navona, and from 1787 and 1795 he built another neoclassical Palazzo Braschi at Terracina, as a private residence for his uncle.
Construction on his Rome palazzo was suspended from February 1798 – 1802 during the Napoleonic occupation of the city, when the French occupied the house and confiscated the recently acquired antiquities Onesti had housed there. Braschi Onesti moved into the palazzo in 1809, when Napoleon declared Rome an imperial city, and was declared mayor of Rome, though the palazzo was still unfinished at his death seven years later.
Some of his antiquities were purchased by the Crown Prince of Bavaria, later King Ludwig I and are conserved at the Glyptothek that he built in Munich.
The Braschi collection included: