Gillian Ansell was born in Auckland, New Zealand, beginning violin and piano lessons at an early age. At 16 she made her concerto debut with the Auckland Sinfonia (now the Auckland Philharmonia).
An Associated Board Scholarship to study violin, viola and piano took her to the Royal College of Music in London where she won several prizes. She then took up a German Academic Exchange (DAAD) scholarship for further study in Germany at the Musikhochschule Cologne with Igor Ozim and the Amadeus Quartet.
In 1987, after working professionally in London for three years, she returned to New Zealand to become a founder member of the New Zealand String Quartet. After 20 months in the second violin seat, she took up the position of violist of the group.

In 2001 she became Artistic Dirctor, with fellow Quartet member Helene Pohl, of the Adam New Zealand Festival of Chamber Music.