Lords of the Realm III is an RTS game set in the medieval era. Players begin by selecting a character by choosing one from the default characters or by making a new one. The characters or nobles serve as the user accounts. Nobles are made up of these customizable features: heraldry, portrait, and house name. After a character is selected, players can opt to play a battle map or a campaign. They can also choose to load a previously saved game. Battle maps become available for each created noble, while campaigns have to be played and completed in sequence.
Players who choose to play the battle map will be put in a battlefield and provided with a number of soldiers. The goal of the battle map mode is to overthrow all enemy forces. The campaigns have three gameplay layers, namely battle, diplomacy, and strategy. The battle layer puts players in the battlefield and gives them manual control over their companies. In the diplomacy layer, players can form alliances and engage in politics and trade. In the strategy layer, players can appoint vassals to their lands and produce units.
This game has four campaigns, set in Ireland, England, Germany, and France. The Ireland campaign has one scenario; the England campaign has five; the Germany campaign has four; and the campaign in France has four.