Gallagher is known for her role as Ellen Smith in The Bill, for her appearances on radio in No Commitments, Salem's Lot, and Memorials to the Missing.
Gallagher later returned to do voice acting for anime with the English dubbed version of the TV series Ronja, the Robber's Daughter.
In 2003, she voiced Amalia, the female lead in Rita Dove's drama The Darker Face of the Earth, opposite Chiwetel Ejiofor in the play's BBC radio adaptation.
[1][failed verification] In 2010, she voiced Fern the Green Fairy, Queen Titania, and Mrs. Walker in the UK version of the movie Rainbow Magic: Return to Rainspell Island.
From 2011 to 2019, Gallagher provided the voice of Nicole Watterson, the title character's mother, on the Cartoon Network animated series The Amazing World of Gumball.