Born in Auckland, Gillian Ansell made her concerto debut as a violinist with the Auckland Philharmonia at the age of 16. At 19, an Associated Board Scholarship took her to the Royal College of Music in London for three years to study violin, viola and piano. She then won a German Academic Exchange (DAAD) scholarship for further study in Germany at the Musikhochschule Cologne with Igor Ozim and the Amadeus Quartet.
After working professionally in London she returned to New Zealand to become a founding member of the New Zealand String Quartet in 1987. She was second violinist for two years before taking up the position of violist.
In 1992, Gillian founded the Adam Chamber Music Festival with a group of friends, performing five concerts in five days. In 2001 she became Cp-Artistic Director with fellow quartet member Helene Pohl.
In 2008 she was made a Member of the New Zealand Order of Merit (MNZM) for her outstanding services to music in New Zealand.
She served on the jury of the Banff International String Quartet Competition in 2019.
Gillian plays on a 1619 Nicolò Amati viola, generously loaned by the Adam Foundation.