He was portrayed by Ryan McDonell.
Stuart Campbell began working for Tess Mercer as an assistant. At the Luthor Mansion, Stuart enters and shows Tess that he's pinpointed the locations of the missing Kryptonians. Later, Tess and Stuart investigated the room in which John Corben awoke in earlier, and saw that the people performing surgery in there were testing something and were possibly still monitoring the test subject to see if it would work. Tess concluded that Major Zod and his people were one step closer to getting their powers.
After Corben's presumed death, Tess examined the Kryptonite heart that served as John's life support, in awe of the power when Stuart reported pictures he has found of Kryptonian symbols that appeared around the world when Zod arrived. He explains that, while their definitive translations aren't known, the designs showed similarities to the Kryptonian words for 'blood', 'nobility' and 'family'. He said hundreds of these symbols have shown up around the world, proving there were many more of Zod's people out there. Finally he showed her the House of El symbol burned into the ground, but with one difference: this Mark of El had a man lying naked in the middle.
At the Luthor Mansion, Tess talked to Stuart who informs her that there was a hacker trying to get through to their systems. Tess tells Stuart to fix the situation or she will have to have him terminated; Stuart looked concerned by this. Tess remained inscrutable as he left to his task. Later Stuart was battling it out in cyber space, with Chloe Sullivan. Chloe was trying to access Tess' files, and Stuart tried to avoid "termination." Clark walked into the watchtower to check on Chloe's progress just as she finishes hacking the 100th firewall protecting Tess' servers.
Just when Chloe feels that she should be getting in, a video of Stuart begins to play, telling Chloe to just give up. He puts his hand in front of the screen. Chloe was only encouraged by this and uses the video to identify Stuart by capturing his fingerprints. Chloe explains that Stuart has crazy computer skills and that she wants to use the information she can gather on him to recruit him away from Tess. Later Stuart walks down an alley and turns, noticing Chloe following him. Chloe tosses down an envelope, which Stuart opens; the envelope contains the information Chloe pulled up on Stuart. She reaches out to shake his hand, Stuart accepts.