On graduating from Edinburgh College of Art in 1954, Blackadder was awarded the Carnegie Traveling scholarship by the Royal Scottish Academy. She subsequently won two further scholarships allowing her to spend her formative years in Southern Europe, particularly Italy. Her early works were landscapes, influence by these trips to Italy, Greece and Yugoslavia.

In 1956 Blackadder married the Scottish painter John Houston. She lectured at Edinburgh College of Art while regularly exhibiting her work, internationally. Blackadder has received many awards, including the Guthrie Award, Royal Scottish Academy (1962) and the Pimms Award for Work on Paper (Royal Academy, 1983). She was joint-winner of the Royal Academy's Watercolour Foundation Award in 1988. She was the first female artist to be elected to both the RA and RSA. She has also received Honorary Doctorates from four Scottish universities. In 2001 she was appointed Her Majesty's Painter and Limner in Scotland.

Since the 1960's she has been renowned for her delicate and yet vibrant still lives, often with flowers. The simplified composition with neutral background is inspired by Japanese art and the use of gold leaf may be indebted to Blackadder's interest in Byzantine mosaics.

Blackadder's work is included in the collections of the Tate Gallery as well as the Scottish National Gallery of Modern Art, among others. Her paintings were also reproduced in a series of Royal Mail stamps.

Public Collections (partial):

Carlisle Museum and Art Gallery
Doncaster Museum and Art Gallery
Dundee Museum and Art Gallery
Glasgow Museum and Art Gallery
Hove Museum and Art Gallery
Kirkcaldy Museum and Art Gallery
McNay Art Museum, San Antonio
Museum of Modern Art, New York
National Museum of Women in the Arts, Washington DC, USA
National Portrait Gallery, London
Perth Museum and Art Gallery
Reading Museum and Art Gallery
Royal Scottish Academy, Edinburgh
Scottish Arts Council
Scottish National Gallery of Modern Art
Scottish National Portrait Gallery
Tate Gallery, London
West Riding County Museum
Wustun Museum, Racine, Wisconsin, USA