Ms. Bjornson's mother brought her daughter to London in 1950. In her teen years, she studied design. Her work in a design school graduate show was noticed by Philip Prowse of the Citizens Theatre of Glasgow and Ms. Björnson was invited to design there.
Plays, musicals and operas would all be a part of her costume and scenic work over the years. She designed the alpine staging of Aspects of Love for London and Broadway, and the Shaftesbury Theatre staging of Stephen Sondheim's Follies. For The Phantom of the Opera — considered to be one of the most complicated design projects in musical theatre history — she won two Tony Awards, for set and costumes, respectively. Her work on the show was replicated in stagings around the world, and she meticulously oversaw aspects of each production and was known for visiting each version.
Her credits include Der Rosenkavalier, Don Giovanni, Donnerstag aus Licht and Tales of Hoffman for the Royal Opera House; Die Valkure and The Gambler for English National Opera; The Queens of Spades for Nederlandser Opera; Katya Kabanova and Jenufa for Houston Opera.
She designed Houston Opera's upcoming world premiere of The Little Prince.
In the ambitious Phantom, Ms. Björnson created opera pastiche settings (a giant elephant hull punctuates the fake opera, Hannibal); a fog-covered, candlelit underground lake on which the title character's skiff glides; and a large staircase at the Paris Opera House, with New Year's Eve revelers hiding behind ornate masks (they sing "Masquerade" as they step down the stairs; some theatregoers note there are also costumed dummies on the steps, but the design work and the overall staging are so rich that the illusion of a crowd works).