하비 길렌

Guillén is the son of Mexican immigrants. He adopted the name Harvey when school teachers could not pronounce his first name. Guillén attended Citrus College, completing the three-year Citrus Singers program in 2005. His father, who was the first person who encouraged him to pursue acting, died of lung cancer in 2017.

Guillén speaks Spanish, English, and Japanese—the last acquired during a 13-month visit to Japan. He identifies as queer.

Guillén at the 2022 Phoenix Fan Fusion

Guillén has appeared in recurring roles on television series such as Alistair Delgado on Huge (2010), Cousin Blobbin on The Thundermans (2013–2018), George Reyes in Eye Candy (2015), and Benedict Fenwick on The Magicians(2017–2018). He also appeared in the 2013 film The Internship.

Beginning in 2019, Guillén played the role of Guillermo, the vampires' human familiar, in the FX television series What We Do in the Shadows. He was set to appear in Quibi's science fiction drama series Don't Look Deeper before the platform shut down in December 2020.

Guillén has received considerable acclaim for his role as Guillermo. TheWrap included Guillén in a list of "2019 Emmy Contenders". Hank Steuver, in his review of What We Do in the Shadows in The Chicago Tribune, stated that Guillén "provides at least half the big laughs" in the show.

Guillén provided the voice of Funny the Magic House in Mickey Mouse Funhouse. He played Nightwing in season 3 of Harley Quinn.

In 2022, Guillén provided the voice for the comedic sidekick character Perrito in Puss in Boots: The Last Wish.

In 2023, Guillén appeared on The Late Show with Stephen Colbert in a skit as Representative George Santos.

In 2024, Guillén reprised his role as Cousin Blobbin from The Thundermans in The Thundermans Return. He also provided the voice of Odie in The Garfield Movie and played Vassago in Helluva Boss.