5.1
Octavius and Antony, located on a battlefield in Philippi, have just learned that Brutus and Cassius are marching to their location. A messenger arrives and tells both generals that the enemy is so close that they must do something quickly. Antony orders Octavius to, "lead your battle softly on / Upon the left hand of the even field" (5.1.16-17). Octavius contradicts him, and decides to march on the right hand side. Antony is annoyed by this, asking, "Why do you cross me in this exigent?" (5.1.19). Octavius replies, "I do not cross you, but I will do so" (5.1.20). Brutus and Cassius arrive at the head of their army. Octavius asks if he should give the sign of battle, and Antony says, "No, Caesar, we will answer on their charge" (5.1.24). The generals all meet and start to insult each other. Antony accuses Brutus and Cassius of being "villains," whereas Cassius tells Brutus that they would not have to listen to Antony now if he had been allowed to kill him as he originally wanted to. The men refuse to back down and they are forced to return to their armies and prepare for battle.
Cassius calls Messala over and tells him that this battle is similar to the one Pompey fought (and lost to Caesar). He points out that although not normally superstitious, he is upset by the fact that two eagles who accompanied the army all the way from Sardis have been replaced by crows and ravens, symbols of bad things to come. He ends his speech by stating, "Our army lies ready to give the ghost" (5.1.88).
Cassius then talks to Brutus and asks him what he will do if they should lose the battle. Brutus rejects suicide, but also tells Cassius that he will never be dragged through the street of Rome as a prisoner. The two generals say farewell to one another and return to their respective armies to prepare for battle.
5.2
The battle has started and Brutus gives Messala orders to take to Cassius. He tells Messala to inform Cassius that he needs to advance faster in order to catch Octavius' flank that is not fighting very well.
5.3
Cassius is upset because he is afraid his men are running away from the field of battle. He tells Titinius that he personally killed his standard-bearer who was trying to run away and took up the banner himself. Titinius informs him that Brutus "gave the word too early" (5.3.5) and that his soldiers quickly started looting the enemy camp once they captured it. In the meantime, Antony's army has been able to surround Cassius.
Pindarus arrives and tells Cassius to run further away. He informs his general that the tents have been taken and are burning in the distance. Cassius sends Titinius to check on some soldiers and find out if they are his men or not, and simultaneously sends Pindarus up a hill to watch and see what happens. Pindarus tells him that Titinius is captured by the troops. Cassius calls Pindarus back down from the hill and hands him the sword with which he stabbed Caesar. He tells Pindarus to take the sword and stab him with it. Pindarus obeys and kills Cassius on the spot before running away himself.
Titinius and Messala return to where Cassius is lying. Titinius has a wreath of laurels on his head, a sign of victory, and is telling Messala that Brutus has defeated Octavius but Antony has conquered Cassius' army. He sees Cassius on the ground and realizes that Cassius was confused about the events taking place on the battlefield. Titinius sends Messala to Brutus to tell him what has happened. He then turns to Cassius' body and says, "Alas, thou hast misconstrued everything" (5.3.83). Titinius then picks up Cassius' sword and kills himself.
Brutus arrives and sees the two dead bodies lying on the ground. He remarks, "Oh Julius Caesar, thou art mighty yet" (5.3.93). Brutus quickly recovers from the loss of his confederate and immediately orders the soldiers to prepare for another battle, this time against Antony.
5.4
Brutus appears again, still leading his troops. He tells his men to continue fighting and leaves them in the midst of battle. Cato valiantly fights but is killed. Lucillius pretends to be Brutus and challenges the soldiers, but he is quickly captured. The soldiers send for Antony, thinking they have finally captured
Brutus. Antony arrives and recognizes Lucillius and tells his soldiers that although they did not get Brutus, they still captured a nobleman. He orders his soldiers to continue fighting.
5.5
Brutus arrives accompanied by several stranglers from his defeated army. He first asks Clitus and then Dardanius to kill him so that he will not be captured. They both refuse and go to stand away from him. He then asks Volumnius to kill him as a friend, but Volumnius tells him, "That's not the office for a friend, my lord" (5.5.29). At the sound of another call to battle, Brutus hastily gets up and orders his men to flee ahead of him. He keeps Strato with him, and finally convinces Strato to hold the sword while he impales himself upon it.
Antony and Octavius arrive with their army. They find Brutus dead on the ground and Strato nearby. Strato informs them how Brutus died, and Antony comments about Brutus, "This was the noblest Roman of them all" (5.5.67). He says that of all the conspirators only Brutus really believed that he was killing Caesar to uphold the Roman Republic. Antony continues, saying, "his life was gentle, and the elements / So mixed in him that nature might stand up / And say to all the world 'This was a man'" (5.5.74). Octavius orders the body to be placed in his tent and gives the order to cease fighting. He ends the play with the lines, "So call the field to rest, and let's away / To part the glories of this happy day" (5.5.79-80).