Finally, the palace was built next to the castle in the second half of the 1760s, the work of which was completed in the 1770s. Based, once again, on the plans of Jakab Fellner. The building was erected by Ferenc Esterházy (IV), who, just like his father, worked as a diplomat also. Shortly after the construction was completed, the Count was able to serve as host of the ruler, who did not simply come here as a visitor. In 1809, French Emperor Napoleon Bonaparte gained victory at Wagram, so he was forced to flee with the court of Emperor and King Francis I. The Emperor spent several months at the palace preceding the peace treaty, and signed the Treaty of Schönbrunn here, on 14 October 1809.
The next owner of the palace was Chamberlain Count Miklós Esterházy (III). Although the Palace of Csákvár was his favourite place to reside, after it was shaken by an earthquake, he spent a long time in Tata. This was where, along with his French wife, Marie Françoise de Baudry, Marquise de Roisin, he entertained Marie Thérèse, Duchesse d’Angoulême, who was the only surviving daughter of French king Louis XVI, and wife of French king Louis XIX. As Napoleon stated about her in connection with the Bourbons: “she is the only man in the family”.