Mariëlla Devos graduated in 1994 from the Fashion/Theatre costume department of the Royal Academy of Fine Arts Antwerp. She was laureate of the Inno/Roularta prize and laureate at the Herren Modewoche in Cologne. She started as a freelancer in fashion and worked for two years in the shoe industry. After the clothing and styling supervision of film and publicity productions she also became active in the world of theatre.
As head wardrobe, assistant costume designer and then designer and creator, she worked for several productions of the Royal Ballet of Flanders and for several major international musical productions. She also collaborated in opera and theatre productions in Belgium and abroad.
Mariëlla Devos is a member of the research council but, besides being a promoter, she is also active as a researcher herself. The research project "Archive Alive", in collaboration with the MOMU and with the help of crowdfunding, led to a permanently accessible archive of the fashion of the 20th century.
Since 2000 she also teaches 3D design sculpting at the Academy of Fine Arts Antwerp in the Theatre Costume department, where she was departmental coordinator from 2007 to 2017. Since 2017 she is also Head of the Applied Arts Programme (Fashion, Costume Design, Jewelry and Graphic Design).