Barnes was a loose cannon who acted without thinking at times. Barnes was very close to John Connor and served in Connor's chain of command.
Following an attack on the Skynet VLA, Barnes learned that Jericho, his brother, was killed following the accidental tripping of a booby trap. He frequently worked alongside John Connor in mission planning and even disregarded a direct order from General Ashdown to remove Connor from command after Connor deemed the attack on Skynet Central to be too risky.
Barnes had also accompanied John in testing the deactivation signal in the field. Under the cover of darkness, the two managed to lure and successfully deactivate an HK-Aerial before destroying it.
He was present with Kate Connor when it was discovered that Marcus Wright was a Terminator and quickly knock him unconscious. Barnes would serve as the first watchman of Wright and discussed with the machine his views on God and how Wright and Skynet were the devil. During this, he used the "machine" as target practice until being tricked by Blair Williams to leave her alone with the machine. Upon finding the truth, Barnes returned to the silo and fired on both Wright and Blair claiming that she had made her choice.
After the destruction of Resistance Headquarters by the machines, Barnes went with Kate Connor on her mission to rescue John from Skynet Central. He helped Marcus to carry Connor to the helicopter for evacuation.