Nan, who was born in Dumfries, was the eldest of the three children of Chris and David Fergusson who lived in Maxwelltown, Dumfries, having designed and built their home in Rotchell Road in the Art Nouveau style. Nan was awarded a travelling scholarship by the college to France and Italy in 1935 where she completed many fine paintings, particularly in Florence and Venice. She later exhibited at Th
e Society of Scottish Artists, The Royal Scottish Academy, the Glasgow Institute and the Empire Exhibition of 1938. In 1937 Nan married James Henderson (1908 -2007), whom she had met at the Edinburgh College of Art, and shared with him a number of exhibitions in Edinburgh, notably at Parson's Gallery, 54 Queen's Street in 1936. She continued to contribute to major exhibitions after the Second World War. While resident in the Borders she helped to found the Galashiels Studio Club in 1949, along with her husband who was then Head of Art at Galashiels Academy. For many years in the 1950s and 60s Nan participated in a seven women exhibition at 116 George Street, Edinburgh during the period of the Edinburgh International Festival. She was passionate in her craft and painted mainly still lives and landscapes in oil. Her works received regular and favourable critical attention in the Scottish Press, particularly from Sydney Goodsir Smith, Art Critic of the Scotsman in the 1960s. He wrote “Nan Fergusson's pictures are always interesting to look at: they have a dry masculine strength that singles them out from any group of women painters. Her two pictures of Aberdour I thought particularly impressive – highly simplified, using a heavy, flat impasto, and patterned almost to a negation of solidity. These are two of the best of her works I have seen.”
From 1963 until 1971 Nan was a much loved teacher of Art at George Watson's Ladies' College alongside her husband, Jim, who was Principal Teacher of Art. During this period she was a regular contributor to the Society of Scottish Artists and the Royal Scottish Academy.