The former 'Breaking Bad' star will be a series regular in the upcoming third season of the dystopian drama, but it's not clear what part he will be playing.
His casting comes after showrunners Lisa Joy and Jonathan Nolan recently promised a "radical shift" in the next set of episodes after most of the hosts from the first two seasons died or left the park.
Jonathan said recently: "I think it's a radical shift. What's compelling and appealing about these characters is that they're not human.
"As we said in the show, humans are bound by the same loops the hosts are, in some ways even smaller. You couldn't expect human characters to withstand and survive the kind of story that we're telling.
"The hosts have a different version of mortality, a different outlook. I think clearly with Dolores, as she's laid out, there is a longer view here, a larger set of goals.
"They're existential. They span aeons. And that's a fascinating level of story to engage in."
Lisa added: "It really is like repiloting."
Jonathan agreed: "Yeah. And that's terrifying and exciting in equal measure. I'm just thrilled that we have this incredible group that we're working with to build it."
Aaron can next be seen in Apple's upcoming anthology series 'Are You Sleeping?', for which he has a one-year contract.
The 39-year-old actor and his wife Lauren Parsekian welcomed daughter Story into the world six months ago and he recently admitted the little girl had strengthened the bond he has with his spouse.
He gushed: "It's amazing. You can't imagine that you could love each other even deeper than you already do. But I think it's just so cool, you know? We weren't blood-related before, but now there's this human that we're both related to and it makes us family in a new way, which I think is so special."