Sophie Aldred was born in Greenwich, London, but grew up in nearby Blackheath. She sang in the church choir of St James', Kidbrooke and attended Blackheath High School from 1973 until 1980, before enrolling as a drama student at University of Manchester. She graduated in 1983 and decided to embark on a career in children's theatre. She also sang in working men's clubs around Manchester.
In 1987, she was cast as Ace in Doctor Who, initially for "Dragonfire", the final story of the series' twenty-fourth season. Her tenure on the show spanned the last nine stories of the programme's original run, which ended in 1989.
Both before and since Doctor Who, Aldred has had a varied and busy television career, particularly in children's programming, where she has presented educational programmes such as Corners, Melvin and Maureen's Music-a-grams (which ran from 1992 to '96), Tiny and Crew (which she presented, 1995–99), the BBC series Words and Pictures (since 1992), and also CITV paranormal show It's a Mystery in 1996. She also played the character Minnie The Mini Magician from Series 8 onwards on CITV's ZZZap! between 1999 and 2001.
Aldred has presented and sung in several BBC Schools Radio series, including Singing Together, Music Workshop, Time and Tune and Music Box. She has also performed on radio and in the theatre. She has also reprised her role as Ace in the 1993 30th anniversary charity special Dimensions in Time and the Doctor Who audio plays produced by Big Finish Productions. She was set to reprise her role in Doctor Who: The Movie, but her schedule was full leaving her character's fate debatable.
Throughout the 2000s she has worked extensively as a voice-over artist for television advertisements, and has also provided voices for animated series such as Bob the Builder, Sergeant Stripes, the UK dubbed version of the CGI animated version of the Australian TV series Bananas in Pyjamas, El Nombre, Peter Rabbit, Noddy in Toyland, The Magic Key and Dennis & Gnasher.
In 2012 Aldred provided the voice of Tom in Tree Fu Tom, a BBC children's series. The series' other main voice actor, David Tennant (who voices Twigs), previously played the Tenth incarnation of the Doctor in Doctor Who. In November 2013 she appeared in the one-off 50th anniversary comedy homage The Five(ish) Doctors Reboot.