This scene is set on the plains of Philippi. Antony and Octavius are with their army, and note that Brutus and Cassius' army is descending from the hills. Brutus, Cassius, Messala, Lucilius and their army enters. Brutus and Cassius go to parley with Antony and Octavius. They fling insults and threats at each other until Octavius challenges them to meet on the field of battle. Octavius and Antony exit with their army.
Brutus and Lucilius speak privately together. Cassius says to Messala that he has seen several birds that day which he takes to be bad omens for their army but also says he is committed to the battle.
Brutus says to Cassius that what they started on the ides of March will end this day. They say their goodbyes in case they do not meet again and separate to prepare for the battle.
Brutus and Messala are on the battlefield amidst sounding alarms. Brutus gives Messala orders, he believes Octavius' army is showing weakness and that his victory is near.
On another part of the battlefield, Cassius and Titinius enter. Cassius complains that soldiers are deserting, and that he had to kill his own ensign. Titinius says that Brutus misjudged Octavius' forces and ordered a charge too early. Cassius forces are surrounded by Antony.
Pindarus enters and urges Cassius to flee since Antony's army has arrived at their tents. Cassius says that he is safe enough where he is, he notes his tents burning in the distance. He sends Titinius away to check if the soldiers coming from the other side of the battlefield are Brutus' or the enemy's. He then sends Pindarus up on the hill to watch what happens to Titinius. Pindarus returns and reports that Titinius was surrounded by soldiers who cheered as he was pulled down from his horse. Cassius mourns Titinius as dead. He gives Pindarus his sword and asks to be killed, in return Cassius says Pindarus will be made a free man. Pindarus stabs him, and flees.
Mesalla and Titinius enter and discuss the situation on the battlefield, Brutus has defeated Octavius while Cassius has been defeated by Antony. They cannot find Cassius, so they split up to search, Mesalla exits. Titinius finds his friend Cassius and, in grief, kills himself.
Brutus and Mesalla enter with others. They discover Cassius' and Titinius' bodies. Brutus laments the loss of “the last of all the Romans” and blames the ill-fortune on the spirit of Caesar at work.
This scene occurs on another part of the field. Brutus, Cato, Lucilius and soldiers enter fighting. Cato and Brutus yell battle cries, Brutus exits the scene. Cato dies and Lucilius is taken prisoner by soldiers. He offers money to the soldiers to execute him and says his name is Brutus. The soldiers refuse the money and call for Antony.
Antony enters and recognizes that Lucilius is not Brutus. Lucilius refuses to give up Brutus' location to Antony and is taken away as a prisoner.
On another part of the battlefield. Brutus, Clitus, Strato, Dardanius and Volumnius enter. They are the remains of Brutus' army. Brutus whispers with Clitus, but Clitus refuses to do what Brutus asks. Brutus then whispers to Dardanius, but Dardanius refuses as well. Clitus and Dardanius speak together and reveal that Brutus has asked them to kill him.
Brutus then calls to Volumnius, a childhood friend of his. He tells Volumnius about the ghost of Caesar and says that it is his time to die. He argues that it is better to “leap in ourselves” than be pushed into a pit. He then attempts to appeal to their past friendship to convince Volumnius to kill him, but Volumnius refuses.
The others plead with Brutus to flee because Antony is arriving. Brutus tells them to go and that he will follow. All exit except Strato and Brutus. Brutus asks him to help him kill himself, and Strato agrees on the condition that he take his hand and say farewell first. Brutus then kills himself on the sword.
Antony, Messala and Octavius enter. They discover that Brutus has killed himself to prevent capture. Antony declares that Brutus was the noblest Roman of them all, and that he was the only conspirator who did not murder Caesar out of personal self-interest. Octavius instructs the soldiers to take Brutus' body and orders that he receive a proper burial.