The first permanent buildings of the castle complex were probably already erected in the 11th century. "Mergintaim" was first mentioned in a document in 1058. In 1219 the three brothers Heinrich, Andreas and Friedrich von Hohenlohe, who had joined the Teutonic Order (Deutscher Orden) after returning from a Crusade, donated this newly founded Teutonic Order their water-surrounded castle and holdings in Mergentheim.
The castle then developed into one of the preferred residences of the Masters of the Teutonic (Deutschmeister), important guests, the Emperor and influential sovereigns were received, extensive, constantly growing property was managed and a wine trade was carried on. With the settling of Dominicans and the sale of possessions of the competing Knights of St. John of Jerusalem (Johanniter), the Teutonic Order increased its economic and political power in the period between the 13th and the 16th century.
Today the palace complex still shows traces of the original medieval water-surrounded castle - the ring-shaped arrangement of the buildings, curved walls of the north wing, fortifications and motes. The castle was expanded in the late 16th century under Grand Master (Hochmeister) Walter von Cronberg after the main residence of the Order was moved to Mergentheim in the course of the Reformation and the Peasants' War.
Over the course of time a representative Renaissance complex was built by connecting the individual buildings in the inner palace courtyard to a closed ring of buildings. In 1574 the main architect, Blasius Berwart, also constructed the spiral staircase between the west and north wing still famous today. The staircase bearing his name appears to be borne by a ring of stone ropes surrounding a hollow space instead of by a newel.
Since 1626 the "Outer Palace" (Äußeres Schloss), a ring of administrative and housekeeping buildings, has been connected to the core of the palace complex. This includes the Main Portal Building (Hauptportalbau), which provides access from the town, the bridge over the defensive trench, the Gate Tower (Torturm), the Chancellery (Kanzlei) and Archive (Archiv) Building, the Royal Stables (Marstall), the Hoop Building (Bandhaus - formerly the Winepress Building (Kelterhaus), the Cooperage and Grain Storehouse (Küferei- und Fruchtspeicher), the indoor riding arena (Reithalle), the barn and the orangery
In the 18th century the wing of the Inner Palace (Inneres Schloss) was remodeled and the Palace Church (Schlosskirche) and the Priests' Seminary were built. In 1739 the "Sala terrena" was erected on the south wing according to plans of the Court Architect Francois Cuvilliés from Munich; a Rococo garden building for festive occasions was built. Only a few garden figures from this building have been preserved and are on exhibit today in the Museum of the Teutonic Order (Deutschordensmuseum).