Louise Brealey (born 27 March 1979), also credited as Loo Brealey, is an English actress, writer and journalist. She played Molly Hooper in Sherlock, Cass in Back, Scottish professor Jude McDermid in Clique, Gillian Chamberlain in A Discovery of Witches and Donna Harman in Death in Paradise.

Education
Born in Bozeat, Northamptonshire, England, Brealey won a scholarship for Kimbolton School and went on to read history at Girton College, Cambridge. She trained at the Lee Strasberg Institute in New York City and with clown teacher Philippe Gaulier in London.

Writing
Brealey has written on cinema, art and music since her teens, contributing reviews and features for magazines including Premiere UK, Empire, SKY, The Face, Neon and Total Film. She is the editor of Anarchy and Alchemy: The Films of Alejandro Jodorowsky (Creation Books, 2007). Until April 2009, Brealey was the deputy editor of Wonderland magazine. A freelance Associate Producer, she has written documentary pitches for BBC Arts. In 2013 her first play Pope Joan was performed by the National Youth Theatre. Her monologue Go Back To Where You Came From was performed as part of Paines Plough Theatre's Come To Where I'm From project in 2018.