Joël Mulachs trained as a voice actress in the early 1990s in Barcelona, her hometown, and later completed her training as actress in New York City, where she attended several acting programs at the Gately Poole Acting Studio and the Actor's Studio.

As a voice actress, Joël Mulachs is the regular voice of renowned actresses such as: Scarlett Johansson, Rachel McAdams, Kerry Washington, Mélanie Laurent, Emily Blunt, January Jones, and Jordana Brewster. These are some of her best-known roles: Black Widow in the Avengers saga, Mia Torretto in the Fast & Furious saga, Maureen Cahill in the Lethal Weapon series and Betty Draper in the Mad Men series.

In 2020, she was awarded the ReTAKE National Dubbing Award for best film dubbing actress for her work in the film Stories of a Marriage, dubbing Scarlett Johansson, an actress for whom she has regularly voiced for more than 15 years.

In addition to her work for Cinema & TV,  Joël has lent her voice to dubbing for the Cartoon, Video Game and Anime industries. These are some of her most outstanding works: Kassandra, in the video game Asassin's Creed Odissey, Riju, in the video game The Legend of Zelda, Cactus in the cartoon series Las Supernenas, Demonika in the Anime series Virtual Hero, Conan in the Catalan dubbed series El Detective Conan & Son Gohan, in the Catalan dubbed series Dragon Ball.

As a voiceover artist, Joël has been working in the advertising industry since 2004, voicing countless campaigns for well-known brands and companies. She is also part of AtresMedia's voice-over team, specifically collaborating since its inception for the television channel LA SEXTA, being the female voice that announces daily promotions of this channel's programming.