Thea Proctor was born in 1879 to a well established family in Armidale, New South Wales. In 1894 she attended Lynthorpe Ladies' College where she won her first prize at the Bowral Amateur Art Society's exhibition.

Encouraged by her apparent skill and the influence of her grandparents, Proctor enrolled in Julian Ashton's Art School in 1896 where fellow pupils included Elioth Gruner, George Lambert and Sydney Long. In 1903 Thea Proctor travelled to London where she studied at St John's Wood Art School with her what was to become lifelong friend, Lambert. The London art scene allowed Proctor to associate with other Australian expatriates including Arthur Streeton, Tom Roberts and Charles Conder. Conder's fan-designs would prove to be a strong influence on Proctor's art making as well as Japanese prints, Ingres drawings and the Ballet Russe. When Proctor exhibited her own watercolour on silk fans at the Royal Academy of Arts she received a warm reception from the arts establishment and critics.

In 1912 Thea Proctor returned to Australia to exhibit in Sydney, Melbourne and Adelaide. Unable to garner to the popularity and recognition she had found in London she returned to England in 1914 where she pursued lithography.

After the first World War, Thea Proctor and Lambert, like many Australian expats, returned to Australia. At first Proctor attempted to popularise lithography with the Melbourne public. When this failed she moved to Sydney and exhibited her own work alongside English lithographs and joined the Society of Artists. In 1925 Thea Proctor held a joint exhibition with Margaret Preston including beautiful coloured woodcuts in vibrant scarlet frames. Despite such displays being considered conservative in Europe, the show was considered 'dangerously modern' in Sydney and the following year Thea Proctor appeared to confirm this affinity and love affair with modernity when she helped found the Contemporary Group, with the aim of encouraging younger, more avant-garde artists.

Creating many beautiful covers for Sydney Ure Smith's The Home magazine, Thea Proctor became an authority on taste, fashion, flower arranging and interior decorating. In 1932 she designed the Lacquer Room restaurant for Farmer & Co and that same year an entire issue of Art in Australia was dedicated to her work.
Thea Proctor taught at both Ashton's Sydney Art School and for the Society of Arts and Crafts, introducing many students to the art of linocut printing as well as designing and producing theatre decor during the 1940s.
In her later years she continued to encourage young artists and was active until her death stating 'I am not the sort of person who could sit at home and knit socks'.