He is best known for his role as Reginald "Bubbles" Cousins on the HBO crime drama series The Wire, and his appearances on Fringe, Party Down, How to Make It in America, and the 2013 film The Spectacular Now.

[5] Royo is mostly known for his starring role on the HBO crime-drama series The Wire as the drug addict and confidential informant Reginald "Bubbles" Cousins, a regular character since the show's first season.

In October 2009, Royo was featured at a Harvard University panel discussion along with fellow actors from The Wire Sonja Sohn and Michael K. Williams.

Later that year, he was a guest star in the third season premiere as well as the seventh and eighteenth episodes of the Fox television series Fringe, playing a cab driver in the parallel universe.

[7] In 2012, Royo appeared in the NBC police drama Prime Suspect as Santana Cordero, an accused murderer killing witnesses before he was tried.

Royo was a guest, playing Otis in the episode "Trading Faces" on Paul Scheer's action comedy series NTSF:SD:SUV:: on Cartoon Network's late-night block Adult Swim.

In 2015, Royo appeared in Agent Carter series portraying Spider Raymond, who ran the night club "La Martinique", but he became more notorious for being an illegal trader.