200 years ago Secularization changed the German Southwest. Following the Napoleonic wars, the buildings, landholdings and property of the monasteries and bishoprics passed into state ownership. The repercussions are felt up until today, as new uses had to be found repeatedly for most of the empty buildings. Mannheim Palace was also affected by the closure of religious institutions and the takeover of church property.
Napoleon dissolved the Palatinate Electorate in 1803. The regions on the right-hand side of the Rhine, including Mannheim, fell to Baden. Mannheim Palace – residence of the Wittelsbach dynasty from the Palatinate since 1720 – became the possession of the grand dukes of Baden. Parts of the Palatinate Electorate collections and the furnishings were taken to Munich. Elector Carl Theodor, who had become the successor to his Bavarian cousins in 1778, had moved from Mannheim to Munich with his Court. In 1804 the dethroned King of Sweden Gustav IV, who was married to a princess of Baden, stayed at the palace. For this purpose the antiquated rooms in the palace had been decorated with new wall paper, tapestries and furniture form the palace inventory. Until 1806 it was only used for occasional stays.
From 1806 to 1811 the newlyweds Archduke Karl von Baden and Stephanie de Beauharnais lived in the palace. As Stephanie was Catholic, she had the house chapels in the palaces in Karlsruhe and Mannheim refurnished. Items from the Secularization such as liturgical utensils from the stocks of the silver chamber, the Church of St. Mary (Liebfrauenkirche) and the Court Church (Hofkirche) in Bruchsal, the treasure of the cathedral in Speyer as well as liturgical vestments of the Commendam of the Knights of St. John of Jerusalem (Johanniterkommende) in Heitersheim. Stephanie first returned to Mannheim Palace as the widow of the Grand Duke in 1819, lived in the former royal chambers in the western wing and had a magnificent royal household.
After Stephanie's death in 1860, the royal household was disbanded. Various uses of the palace followed, i.e. as a school and barracks, for offices like the High Manorial Court (Oberhofgericht) of Baden, the Lower District Court (Amtsgericht) with the prison (Amtsgefängnis), the district attorney with the plain-clothes police, the notary's office and government apartments. The cellar rooms were used for storage purposes for the remaining art collections of the Palatinate Electorate. After Grand Duke Friedrich II had signed the abdication of the Baden dynasty in 1918, the palace was the property of the Free State of Baden. In 1926 the Palace Museum (Schlossmuseum) opened. The magnificent palace appointments were removed for storage in 1944 before bombing raids destroyed Mannheim Palace in WWII. The Library Cabinet (Bibliothekskabinett) was the only room out of over 500 that remained undamaged.
With the exception of the roof, the state rebuilt the palace according to the historical example in 1947. The original layout of the interior rooms was completely changed with the exception of the Palace Church (Schlosskirche), the staircase and das Hall of Knights (Rittersaal). The District Surveyor's Office (Bezirksbauamt) moved into the palace in 1948. The local tax office (Finanzamt), the regional court (Landgericht) and the College of Economics (Wirtschaftshochschule) were then added. Since 1967 (the College of Economics had meanwhile been raised to the status of a university) the palace has been the seat of Mannheim University.