Justine Marsden began piano studies at the Sydney Conservatorium with Nancy Salas, followed by violin studies with Alice Waten. She attended the Conservatorium High School, where she studied viola with Winifred Durie and Alex Todicescu, and completed her Bachelor's degree with Merit at the Sydney Conservatorium in 1984.
From 1985, she continued postgraduate studies in Berlin for four years with Wolfram Christ. During her time in Berlin, she played as a casual member of the Berlin Philharmonic Orchestra and the Berlin Radio Symphony Orchestra and was a member of Ensemble Oriol Berlin. She performed as soloist with the Baden-Badener Philharmonie and as principal guest violist of the Orchestra of the Berliner Kammeroper.
Justine Marsden returned to Australia in 1989 and joined the Australian Chamber Orchestra, with whom she occasionally acted as Principal Viola. She has also worked as both a soloist and orchestra member with the Australian Brandenburg Orchestra. From 1991 to 1993, she was a member of the Novalis Quartet and has performed as guest artist with the Ku-ring-gai Virtuosi and the Grevillea Ensemble. She has recorded music by Margaret Sutherland with her sister, violinist Marina Marsden, with whom she also performed Mozart's Sinfonia concertante with Orchestra 143 in 2004.
Justine has been a member of the Sydney Symphony Orchestra since 1990, acting as Associate and Assistant Principal Viola on occasion. In 2004, she was awarded a Sydney Symphony Friends and Michael and Mary Whelan Trust Scholarship to further her viola studies with Wolfram Christ in Germany and to research issues relating to musicians' health at the Kurt Singer Institute in Berlin.