Adshead was born in London. She was taught watercolour painting by her father Stanley, an architect and Professor of Civic Design at the University of London. She spent 1919-20 in Paris, then attended the Slade School of Art under Professor Henry Tonks from 1921 to 1924. In 1924 Tonks arranged her first mural project with Rex Whistler, who was a fellow student, at the Highways Club, Shadwell. This project led, in 1925, to a commission to decorate a dining room for Professor Charles Reilly in Liverpool. The decorations were exhibited at the Royal Institute of British Architects in 1926, before their final installation. They are now on display at Liverpool University. In 1929 she married the artist Stephen Bone, son of the well known artist and etcher Sir Muirhead Bone. The couple made many painting and sketching tours through Europe.
Exhibitions in which she participated include the Applied Art Exhibition at the Whitechapel Art Gallery, 1926, and the Art in Industry Exhibition at Burlington House, 1935. She exhibited regularly at the Royal Academy from 1927, and with the Women's International Art Club from the mid-1930s, serving on their Committee in 1951. In 1930 she held a solo show at the Goupil Gallery, and was elected a member of the New English Art Club that year. She had solo shows at Sally Hunter & Patrick Seale Fine Art in 1986 and 1989.
In 1931 Adshead began a series of drawings and watercolours of the Crystal Palace, London. She and Bone produced murals for Cunard's liner Queen Mary in 1935-6, but they were not installed. In 1937 she produced wall panels to decorate the British Pavilion at the Paris International Exhibition. She produced stamp designs in 1949, 1951 and 1953. In 1952-3 she and Bone organised and taught at Dartington Summer Painting School. From 1953 through the 1960s she was Secretary of the Society of Mural Painters. In 1957 she painted a triptych for St Mary and All Angel's Church, Plymstock, Plymouth. Her growing interest in mosaic design led her in 1962 to study at Ravenna and in Sicily, and to take a course in the techniques of Italian mosaic design at Kingston Art School. In 1966 she produced a decorative pool in mosaic, marble, stones and cable sections in the Telephone Exchange Courtyard, Guernsey. In 1983 she embarked on a major mosaic mural project for a pedestrian subway in Rotherhithe, London. In the 1980s and 1990s she made sketching tours in Malta, Turkey and Madeira.
Her numerous public and private mural commissions include decorations (no longer extant) for London Underground for Bank Station (1926) and Piccadilly Circus Station (1928), racing murals for Lord Beaverbrook (1928), murals for Vauxhall Motors, Westminster Hall, and Luton Hoo House in the 1940s, decorations for Selfridges restaurant (begun 1949, destroyed 1967), and designs for the Ministry of Works (1954) and the Commonwealth Institute (1967). She also produced London Underground posters, and magazine and book illustrations, including The Little Boy and his House and The Silly Snail by her husband, and her own Travelling with a Sketch Book (1966).
Mary Adshead, exhibition catalogue, Sally Hunter & Patrick Seale Fine Art, London 1986
Katy Deepwell (ed.), Ten Decades: Careers of Ten Women Artists born 1897-1906, exhibition catalogue, Norwich Gallery, Norwich 1992