The play opens with a dispute between Henry Bolingbroke, Duke of Hereford, and Thomas Mowbray, Duke of Norfolk. Bolingbroke has accused Mowbray of treason, and the two of them exchange insults in the presence of King Richard. After attempts to reconcile them fail, Richard orders them to take part in a traditional chivalric trial by combat. On the field of combat, the king changes his mind and banishes the two men — Bolingbroke for ten years (commuted to six) and Mowbray for life. Then the king makes plans to leave for the wars in Ireland.
Before departing, Richard visits the ailing father of Bolingbroke, John of Gaunt, Duke of Lancaster. Gaunt warns Richard with his dying words that he is flirting with danger and doing great harm to the country by allowing himself to be influenced by his sycophantic courtiers. When he dies, Richard takes possession of all of Gaunt's wealth and leaves for Ireland.
Unhappy with Richard's incompetence as a ruler and worried by his seizure of the Duke of Lancaster's wealth, a number of nobles rally support for Henry Bolingbroke. When Bolingbroke and his army decide to return from exile in France, the rebel forces prepare to confront Richard on his return from Ireland.
The rebel noblemen force the king to abdicate, and Bolingbroke is crowned as Henry IV. Richard is imprisoned in Pomfret Castle, where he faces his death alone, philosophically contemplating the meaning of his fall from grandeur. Sir Pierce of Exton decides solely on his own to execute the deposed king, and then, as a result, he is banished by King Henry. The play ends with Henry IV planning a penitential pilgrimage to the Holy Land.