Role in the film
Garsiv first appears alongside his brothers Tus and Dastan leading his father's forces in a war on the Kosh. After a spy informs Nizam that the Holy City of Alamut has been providing the Kosh with weapons, Nizam convinces Tus, the leader of the army, to go into the city and crush it, despite King Sharaman's desire for it to be left in peace. Dastan protests, but Garsiv and Tus listen to their uncle Nizam instead. Dastan wants to lead the attack but Garsiv claims that he wants the first blood. Tus tells Dastan that he is not ready to lead the attack. The group begins firing catapults of flaming rocks toward the city. Dastan disregards Tus's orders and leads his own gang of warriors through the East gate of the city. Bis and Dastan's other troops shoot arrows above Dastan so that he can climb into the city. Dastan opens the East Gate and takes on the “Impossible Gate” by climbing up a tower and entering from above. He notices Alamutian soldiers charging towards his men, so he knocks over a large bowl of boiling oil and ignites it to create a barrier of flames.
Tus and Garsiv are impressed by Dastan's daring, and they decide to confront the Princess and Tus declares his intention to marry her to keep the peace between Persia and the people of Alamut. In the banquet, Dastan presents his father with the robes of the regent. His father tells him that he is proud of him but that Dastan hasn't learned that a real leader does what he has to in order to defend what he knows is right. Dastan asks his father to allow Tus to marry Tamina, but King Sharaman points out that Tus has many wives. Since Dastan has none, King Sharaman gives Tamina to Dastan as his first wife. Dastan is shocked and can barely speak before his father starts screaming. The robes of the high regent were covered in poisonous acid which eat away at the king. Garsiv tries to rip them off while Dastan screams for help but Dastan appears to be a murderer. His father's guards move to capture him, but Bis jumps to his aid and fights them. Bis is quickly killed but Tamina leads Dastan out of the palace. They escape the city on horseback with Garsiv in pursuit.
Nizam later talks to Tus and Garsiv about what should be done with Dastan. Tus wants to put him on trial, but Nizam tells him that Dastan should be killed and not allowed to return; otherwise his accusations could destabilize the region. Garsiv is suspicious of Nizam's desire to have Dastan killed but says nothing. Tus tells him that Dastan will be put on trial and ends the discussion. Garsiv and his men arrive at the village and he takes Dastan in doors. Dastan makes his case and tells him that Nizam is the one who killed their father. Garsiv tells Dastan what Nizam told them, confirming that he believes Dastan. However, the Hassansins arrive and attack the Sheik's men. In the onslaught, Tamina is knocked out and the dagger is taken, Garsiv is killed and the surviving Hassansins escape.
Garsiv later appears after Dastan altered the timeline, watching as Dastan decries Nizam a traitor in public, and pursues as Nizam tries to kill Dastan. He later watches as Tus offers Dastan's hand in marriage to Tamina to keep the peace between Persia and Alamut.