He began his career as a child actor, primarily guest-starring on various television programs, including playing BJ Malloy on the Nickelodeon sitcom Sam & Cat (2013–2014), before being cast as Derek Zoolander Jr. in the comedy film Zoolander 2 (2016) and David "Truck" Johnson III in the second season of the Fox series The Exorcist (2017).

Arnold has also appeared in other films such as Hardcore Henry (2015), Runt (2020), 8-Bit Christmas, Diary of a Wimpy Kid (both 2021), Mr. Harrigan's Phone (2022), and Family Switch (2023), as well as voicing Jawbreaker in the Nickelodeon animated series Transformers: EarthSpark (2022–present).

[3] He subsequently had guest roles in the television shows About a Boy, Richie Rich, Bones, Goldie & Bear, Fresh Off the Boat, Veronica Mars, and Outmatched.

[7][3][8][9][10] In August 2017, he was cast in a recurring role as David "Truck" Johnson III in the second season of the Fox series The Exorcist.

[11] Arnold had a starring role as Borgie in the indie film Runt, opposite Cameron Boyce and Nicole Berger.