Dissatisfied with classes at Elam that catered 'for the dilettante', Jean Horsley departed for London's Chelsea School of Art in 1934. Returning a year later, Horsley gained qualifications in physiotherapy, enabling her to travel and work overseas, particularly in America, where she was strongly influenced by the work of Robert Motherwell and Helen Frankenthaler.
Included with M. Rainier and Freda Simmonds in the 1957 Three Women Painters exhibition at the Auckland City Art Gallery, Horsley received complimentary reviews, including the following from the New Zealand Herald critic: "Jean Horsley's strength is…in colour, fresh, sanguine, briskly put on, and unobtrusively supported by a carefully worked out framework. She is clearly one of our major painters." (NZH 17/7/57)
Horsley exhibited extensively, in England with fellow expatriates Ralph Hotere, Bill Culbert and Ted Bulmore. A regular exhibitor with the Auckland Society of Arts from 1935-1938, Horsley was also included in numerous exhibitions at the Auckland City Art Gallery and held a shared exhibition with Louise Henderson at the New Vision Gallery in 1966.
Anne Kirker (author of New Zealand Women Artists: A Survey of 150 years), described Horsley's works produced in the sixties as amongst "the most conscious manifestations of an Abstract Expressionist style in the work of a New Zealand-born artist" emphasising that her "most accomplished statements…helped to generate a greater awareness of abstract modes of expressionism in this country."
The principal curator of Seize the Day: A Tribute to Jean Horsley, (Auckland City Art Gallery 1997), Alexa Johnston, described Horsley's as "An expressionist, working consistently with abstraction, Jean sets paint dancing in canvas, makes light and airy compositions using colours rich and heavily glowing, or pale, evocative and meditative. Her abstract forms allude to movement and transformation. Several of her works have become icons of New Zealand modernist achievement."
The Auckland City Art Gallery's permanent collection holds eleven works by Jean Horsley as well as one Luise Fong work and two works by Saffronn Te Ratana, which they were able to purchase with Horsley's assistance shortly before her death.
Jean Horsley was awarded an O.B.E for her "Services to Art" in 1996.