Through the course of a century Carlo Maderno, Girolamo and Carlo Rainaldi, and Borromini contributed to the architecture of this building. It was erected on the ruins of Nero's baths and sold in 1590 by Monsignor Andrea Vento to the Marquis Vincenzo Giustiniani.

The Giustinianis were great merchant aristocrats from Genova who invented the concept of a trading company comprised of shareholders. When they moved to Rome, they made this palace their family home. They possessed an immense art collection, including more than 1800 ancient statues, some of the most important 17th century paintings and numerous paintings by Caravaggio.
It was here that the Constitution of the Republic of Italy was signed in 1947, and today, it is the residence of the President of the Senate.