A Scottish painter of portraits, flower-pieces, sea-pieces and decorative compositions. From 1936, Walker was a member of The London Group. Her work displays the influence of Impressionism, Puvis de Chavannes, Gauguin and Asian art.
 
Walker achieved considerable success throughout her career, becoming the first female member elected to the New English Art Club in 1900. Walker's works were exhibited widely during her lifetime, at the Royal Academy, the Royal Society of Arts and at the Lefevre Gallery. She represented Britain at the Venice Biennale four times, in 1922, 1924, 1928 and 1930. Although Walker proclaimed that 'there is no such thing as a woman artist. There are only two kinds of artist — bad and good', she was elected Honorary President of the Women's International Art Club in 1932. Soon after her death, she was the subject of a major retrospective at the Tate in 1951 alongside Gwen John and Frances Hodgkins.
 
Walker is now acknowledged as a lesbian artist, a fact which critics have noted is boldly apparent in her preference for women sitters and female nudes. It has been suggested that Walker was one of the earliest lesbian artists to explore her sexuality openly in her works. While Walker was contemporarily regarded as one of the foremost British women artists, her influence diminished after her death, perhaps due in part to her celebration of female sexuality. Made a Dame Commander of the Order of the British Empire in 1943.