Atom was considered for membership during the meeting of the Justice League. Captain Marvel questioned whether his size was a valuable addition to the League, but Batman spoke in the Atom's favor. It was eventually decided that Atom could join.
Still under mind control, Atom was slicing the remaining piece of Starro with a laser scapel, when suddenly, a Starro slice floated. He changed his size to grab it, but in the process was tagged with cure-tech by Miss Martian, and went unconscious.
Atom was one of a number of Justice League members who responded to the emergency in Metropolis. Even at his minimum size, he was unable to get through the force field surrounding the city. He asked Red Tornado for the whereabouts of the other Leaguers.
The alien ship firing an apparently ineffectual beam of energy at the force field caused Atom to realize the field was probably generated from the inside. Nightwing communicated the information to the heroes trapped in the field.
Metropolis December 1, 17:45 EST
Martian Manhunter, the Atom, and the Flash snuck aboard the alien vessel, and were soon approached by the Collector of Worlds. Atom made a futile attempt to attack The Collector while he was distracted, before immediately being spotted and dropped to the ground. The heroes were quickly defeated, and dropped, via a hatch, from the Collector's ship.
After Nightwing contacted Martian Manhunter that they were inside the ship, J'onn lifted Flash and Atom to safety.
The Collector's Ship December 1, 19:01 EST
Flash and Atom made it back inside the ship, and met up with Alpha Squad at exactly the same time as former prisoners of Kylstar, who were teleported aboard. Lagoon Boy used the Bio-Ship's cannon to destroy the coludroid.
Metropolis December 1, 19:03 EST
Dozens more coludroids showed up and surrounded the heroes. Nightwing and Atom persuaded the Collector to shut down the beam that shrunk the city.
Metropolis December 1, 22:03 EST
Back on the ground, Atom listened to Captain Atom and Nightwing as they discussed what to do next.
Dr. Palmer checked in on research from his assistant, Karen Beecher. He greeted Mal Duncan, before taking a look at Karen's work. To compare results against the white dwarf fragment, he committed to several hours of work with her. Mal dismally left without them noticing.
Atom and Bumblebee tried to get Jaime's scarab off his spine by going inside his body. Atom used a laser to try and cut the scarab open, but the defenses proved too tough. They had to be extracted from the body. Once outside and back to normal size, Atom informed Jaime that he didn't think the scarab could be removed without killing him.
When magnetic field disruptors planted by the Reach threatened the Earth, Atom joined 39 other heroes of Earth in a briefing in Metropolis. The heroes would use a computer virus provided by Lex Luthor to safely disable the disruptors. The heroes were paired off with another into twenty squads: one member would run interference against weapons guarding the disruptors, allowing the other to get close enough to plant the virus.
Atom was assigned to Omicron Squad, and worked alongside Tye Longshadow. Within thirty minutes, all squads had succeeded in their mission.
When the Team was summoned to the mission room for a face-to-face meeting with members of the League, Atom was among the leaguers present. Batman informed them that they would now operate side-by-side with the Justice League from the Watchtower. Not because Mount Justice was destroyed, but because they earned the right to do so. The League then left the Team to its own devices.
In the comics, there have been four people with the name Atom: Al Pratt, Ray Palmer, Adam Cray and Ryan Choi. This iteration is Ray Palmer.
This is Ray Palmer's sixth animated appearance. He appeared in Superman/Aquaman Hour of Adventure, Super Friends, Justice League Unlimited, Justice League: New Frontier and Batman: The Brave and the Bold.