Comte de Guiche arrives at the play with his entourage, including the empty-headed Vicomte de Valvert, to whom he wants to marry Lady Roxane.
His first few lines show that he is a proud man who thinks himself above the common folk—including Cyrano and Christian.
After Cyrano meets with Roxane and learns of her love for Christian, de Guiche arrives on the scene to congratulate Cyrano on his defeat of the 100 men last night. During this scene, he admits that it was he who hired them to kill Lignière for writing a satiric song about him.
De Guiche offers Cyrano a position as a playwright for the Cardinal himself, hoping to tempt the enemy to his side with money. Though Cyrano is indeed tempted, he ultimately refuses.
De Guiche hastily leaves when Cyrano gets angry.
Later, de Guiche visits Roxane. He no longer hides his lust for her behind his puppet, Valvert, but tells her straight up that he is leaving to take his troops into battle. He hopes his departure will leave her "cold."
He then tries to impress her by saying he has been made Colonel. Nothing matters to Roxane until she discovers that the regiment that is leaving includes Christian (and Cyrano).
Then she pretends to love de Guiche, advising him on how to avenge himself on Cyrano. This convenient tactic also keeps Christian from going off to battle. De Guiche, blinded by his lust for her, agrees.
He also tells her he would like a tryst with her in a nearby convent that night.
After Cyrano’s moving speech, a Capuchin messenger arrives bearing de Guiche’s note. It asks Roxane to come to the convent as planned earlier. But Roxane has different plans. She finagles a secret wedding to Christian.
Cyrano, given orders to distract de Guiche, carries them out. When de Guiche arrives masked and cloaked to find Roxane, he runs into a drunken madman (an acting Cyrano) whose crazy stories about falling from the moon distract him from his initial goal.
When he discovers that he has been duped yet again, de Guiche finds a way to take revenge immediately. He breaks his promise to Roxane and takes the troops, including Christian and Cyrano, directly to war.
At Arras, the Comte is not well-liked. The soldiers consider him arrogant and cowardly.
He boasts about his bravery, telling the soldiers the story of his escape from the Spaniards. During a scrimmage, he found himself in enemy lines and, thinking quickly, removed his white scarf (a mark of his French military rank) to blend in with the crowd and get away. Cyrano basically accuses him of cowardice and then produces de Guiche’s scarf to add insult to injury.
In an act of revenge, de Guiche reveals some news he has gotten from his Spanish spy. In order to get re-provisioned, the French crown needs a regiment to "buy time" for them. This essentially means sacrificing those men.
De Guiche decides to volunteer Cyrano’s regiment, just to get back at Cyrano. He mocks Cyrano, telling him this is the perfect opportunity for him to "fight one hundred against one."
When Roxane arrives unexpectedly, de Guiche is among the many voices urging her to go home to safety. But she is stubborn. Unable to convince her, de Guiche goes off to check on the guns.
While he’s gone, Roxane reveals enormous amounts of food she has brought for the starving cadets. When de Guiche returns, they hide the food from him.
But he has a surprise up his sleeve. In an unexpected show of bravery, he announces he will fight with the troops because Roxane is staying. He means to defend her and win her love. At this, the cadets decide to share some of their food with him.
But we are never to see whether or not he has any courage. Cyrano, after Christian’s tragic death, entrusts Roxane to de Guiche’s care on the grounds that the man has finally proven himself (by volunteering to stay and fight).
De Guiche bears Roxane and himself back to Paris and safety.
Fifteen years later, de Guiche is still trying to win Roxane—even though she is still in mourning (over Christian’s death) at the convent. He unexpectedly asks for her forgiveness.
In his conversation with Roxane, we learn that he still has no pity for Cyrano and, when he speaks to Le Bret, he "warns" him of a fatal "accident" waiting for Cyrano. This is probably just a veiled death threat.
This is the last we see of Comte de Guiche, but his prophecy ends up coming true—Cyrano dies from an "accidental" wound.