Jazz accompanied Supreme Commander Ultra Magnus and Sentinel Prime to Earth to retrieve Optimus Prime's crew and the AllSpark. When Magnus ordered Jazz to activate a force field around their ship to prevent organic life contamination, Jazz expressed interest in getting a closer look at them. This caused Sentinel Prime to warn Jazz that the organics would eventually spit acidic goo that would melt through his body armor and destroy vital circuitry. Jazz was...less willing to meet the organics after that.
When Sari Sumdac managed to sneak aboard their ship, he tried to send her out without provoking her. When she realized that Jazz was afraid of her, she tried to scare him. After Bulkhead explained that Humans were harmless (and Bumblebee explained that Sentinel Prime was a jerk), Jazz accompanied the Autobots to a Sumdac manufacturing plant that was going haywire, finding a good opportunity to test out his slick new Earth mode as well. Jazz and Prowl managed to keep the AllSpark-powered drones away from Sari and Optimus long enough for Sari to shut down the assembly line. He and Prowl traded several martial arts-centered quips throughout the battle, talking about Metallikato moves like the "Five Servos Of Doom" attack.
When Ultra Magnus started to receive reports of Decepticon uprisings at the rim of the galaxy, Jazz commented that it was probably because they'd "got wind" that Megatron was still online. Later, Jazz noticed a spike in AllSpark energy, and Ultra Magnus took him to investigate, leaving Sentinel Prime to watch Optimus Prime. Their combined attempt to remove the "SmallSpark", which Starscream had booby-trapped, failed, and they were blown off the train in which it was embedded. Optimus and his crew, with the help of Sari and the Key, successfully and safely removed the AllSpark fragment, but Jazz could only watch as they received a dressing-down from Ultra Magnus for becoming involved. Then Starscream himself crashed to Earth, courtesy of Megatron's cannon, and knocked out Magnus. Jazz turned to Sentinel for orders, but the panicking Guardsbot was unable to think of anything. Optimus took over, directing his crew and Sari to various tasks; and himself, Jazz, Sentinel to take down Starscream—although Jazz needed to talk down the posturing pair of Primes before they could get to fighting the bad guy.
His nunchaku proved ineffective, however, and he was swiftly knocked out, leaving Optimus to save the day again. Jazz later escorted Optimus's crew in taking the stasis locked and gagged Starscream to be imprisoned in the Elite Guard's ship, before the three Guardsbots and their ship departed, leaving Optimus and his crew to deal with the remaining Decepticons on Earth. Jazz was present as Starscream escaped the Elite Guard ship.
When Rodimus Prime requested back up, Jazz told him they were trying to hold off some other Decepticons. Later, Ultra Magnus told Jazz and Sentinel to put a team together to go after the escaped fugitive Wasp. He tried to contact reinforcments, when he Sentinel Prime, Jetfire and Jetstorm pursued the "Decepticon spy" Wasp (who was really Bumblebee) on Earth. He and the rest of the Autobots nearly caught Wasp but instead he, along with Prowl discovered that Sentinel was trading Elite Guard weapons for Decepticon captures with a certain bounty hunter. Typical.
When Ratchet defied a direct order from Mr. Jerkface, he was ordered to track them down and bring them in. However, Jazz felt otherwise and helped them on their way. As Ratchet ran off with Ultra Magnus' hammer, Jazz volunteered to go after them. In truth however, Jazz had chosen to throw his lot in with Optimus rather than Sentinel. Presumably, during his time on Earth, Jazz learned or perfected the art of Processor Over Matter with Prowl, in time to use it to help him gather the remaining pieces of the AllSpark in an attempt to stop the booby-trapped Lugnut Supremes from destroying the city.
When that amount proved to be insufficient, Prowl sacrificed his spark to make the difference, over Jazz's pleas. As Prowl's body crashed down, Jazz caught him in his arms, cradling his fallen friend with grief. Optimus Prime later eulogized the fallen Autobot, still in Jazz's arms, with the surviving Autobots. With the Decepticons defeated, Jazz returned to Cybertron a hero, bearing the body of his fellow Cyber-ninja, being promoted to second in command to Optimus Prime. He was also present when Blurr was brought back to life using the AllSpark Matrix.