He was portrayed by Arnold Vosloo.
Marwan hired the Araz family and Omar. After one of his terrorists blew up a train, which was a cover for the true first phase of his plan, Omar's men kidnapped James Heller, the secretary of defense, and his daughter Audrey. He hired Mandy to assist him with this. Heller was to be executed for crimes he did not commit, but Jack Bauer rescued Heller and Audrey.
However, the kidnapping was a cover for Marwan's true plan, to acquire a device called the Dobson Override so he could use it to cause nuclear power plants to melt down, which would kill millions by radiation. All the reactors but one were eventually shut down bu CTU, but Marwan escaped when Jack and Curtis tried to capture him.
Jack had Dina Araz, whom he made a deal with to give her and her son Behrooz immunity from their involvement in Marwan's plan, take him hostage so he could get to Marwan. Marwan tested her loyalty by giving her an unloaded gun and telling her to kill Jack. Dina tried to shoot Marwan instead, so he had his men kill her.
As a distraction from his next attack, Marwan offered to trade Jack to CTU in exchange for Behrooz. They put tracking devices on him, while Marwan intended to kill Jack, but his sniper was killed, and Jack survived the exchange. Marwan found the tracking devices on Behrooz. He also got another of his men, Mitch Anderson, to shoot down President Keeler's plane, severely injuring him. Anderson was presumably killed by US fighters.
Marwan and his men then acquired the nuclear football, a briefcase containing all the firing codes for the US's nuclear warheads. Marwan set up a nightclub as his hideout, and was nearly captured by Jack and his team, but the attempted capture of Marwan failed due to the new president, Logan, arresting Jack for disobeying orders, and Marwan escaped again.
Marwan had his associate, Robert Morrison, launch a nuclear warhead at Los Angeles. He planned to escape in his helicopter, but was found once again by Jack, who was informed of his location by Mandy. CTU's objective was to take him alive so he could tell them the warhead's target. Marwan, knowing there was no escape this time, jumped off the balcony in a suicide attempt, but Jack grabbed onto his hand. Marwan cut Jack's hand to make him let go, and fell to his death.
Fortunately, CTU found information inside Marwan's helicopter that said where the warhead would strike, and it was shot down before it could detonate and destroy Los Angeles.