Robertson was born in Manchester, England. After leaving school she looked after her mother who suffered from rheumatoid arthritis. Robertson's father, the journalist Fyfe Robertson, gave her a second-hand camera in 1949 and the following year she had a photo story about her sister doing her homework published in Picture Post.
Over the next few years she had several photo stories published in the magazine including "Sheep Shearing in Wales" (1951), "Tate Gallery" (1952), "Mother's Day Off" (1954) and "Childbirth" (1955).
Robertson was appointed an OBE in 1999. She is the widow of the Picture Post photographer Thurston Hopkins (1913–2014).
As well as photojournalism for magazines such as Life, Robertson worked in advertising.