The only daughter of Collett Dobson (actor-manager) and his wife Harriett, Agnes Dobson was descended from a family of explorers who included Captain Collett Barker. She once wrote described her parents as itinerant actors and recalled that she had been 'brought up in theatre trunks, cradled on the hat-rack of trains.' At the age of 10 days old Dobson made her stage debut as Moses in the bullrushes, and went on to play a number of child roles. In the early twenties she was a pioneer in Australian silent movies. Her first husband, actor/playwright Ronald Riley, was also a member of a notable theatre famil. Dobson, her parents and Riley were all members of Fuller's Damatic Players around the same period.
Through the 1920s and early 1930s Dobson acted in Sydney and Melbourne productions, then moved to Adelaide where she lived for the next 10 years, acting with the Ab Intra Studio Theatre, the Adelaide Repertory Theatre, the Esmond George Players and the WEA Little Theatre. She founded the Independent Theatre Group, which ran in Stow Hall, and become a director and teacher of considerable influence. During this time she wrote several plays.
Dobson returned to Sydney after WWII to work as a freelance actress, writer and director. She became Principal of the Hector Crawford School of Broadcasting and Television and secured employment in radio as an actress, producer and writer. She also reviewed books under the pseudonym 'Agnes Grey,' and was Mrs Sharpshott on the Village Glee Club (ABC) for over 20 years. Dobson continued to appear in both Australian films and television during the 1950s and 1960s.