Fanny Westerdahl was engaged at the Royal Dramatic Theatre in 1829 (at age 12) and made her proper debut in 1831, as "Carolina" in Baschan in Suresne.

[3] In 1849, she was referred to as the only one of the actresses of the royal stage truly suited for "great drama" and praised her for her natural warmth and "mild passion".

During a performance in which she played a bandit, she was to shoot her co-actor Georg Dahlqvist, but when the gun did not work as it should, she hit him with it, which caused him to faint for real.

"[3] At this point, she was described as overweight, a drunk and with a frivolous mouth, but talented in comedy, and she was recommended by August Bournonville as an example of good instinct and fantasy in contrast to mere education.

Her best-known roles include: "Louise" in Kabal and Kärlek, "Johanna af Montfaucon" or "Griselda", Amalia in Röfvarbandet, and "Katarina Månsdotter" in Erik XIV.