He serves as a consul and leads the Roman army. A thoughtful individual, he usually speaks with care and caution, though he occasionally indulges in grandiose language. He is more practical than idealistic but remains loyal to Rome and his friend Coriolanus. When a conflict arises between his nation and his friend, Cominius finds himself in a difficult position. His attempts to mediate between the two sides ultimately fail.

Like other patricians in the play, Cominius is constantly worried that the fragile balance between social classes will crumble, potentially plunging Rome into civil war. During a violent clash in the marketplace in Act III, Scene i, Cominius reprimands the tribunes and the plebeians. He warns them, "That is the way to lay the city flat, / To bring the roof to the foundation" (III.i.203-04). Cominius understands that the senate cannot simply impose its choice for consul on the common people; they must be persuaded and won over. In Act III, Scene ii, lines 93-95, he advises Coriolanus that unless he can stay calm when returning to the marketplace, he should not go at all. When Coriolanus admits he cannot pretend to be humble and contrite, Cominius reassures him, "Come, come, we'll prompt you" (III.ii.106). Cominius believes that effective politicians sometimes need to compromise and that the Roman republic's structure requires respecting the power of the common citizens.

Cominius's tendency to embellish is most evident in his speeches praising Coriolanus. Before the senators vote on Coriolanus's election to the consulship, Cominius vividly recounts Coriolanus's impressive military career. Although he claims, "I shall lack voice" (II.ii.82) to fully convey his merits, he rises to the task. In an elaborate speech filled with vivid descriptions, complex sentences, and imagery, he portrays Coriolanus as a superhuman hero (II.ii.82-122). Likewise, after Coriolanus is banished and joins the enemy forces, Cominius reports that the Volscians have made Coriolanus "their god" (IV.vi.90). Again, he suggests that Coriolanus is more than human: "He leads them like a thing / Made by some other deity than nature" (IV.vi.90-91). When Cominius returns to Rome after trying to dissuade Coriolanus from attacking the city, his description of Coriolanus inspires awe: "he does sit in gold, his eye / Red as 'twould burn Rome" (V.i.63-64). Through his words, Cominius significantly enhances Coriolanus's image as a superhuman force in the play.