Born in Nottingham, the son of architect and sometime painter, William Knight, Harold won a travelling scholarship while at the Nottingham School of Art, allowing him to study at the Academie Julian under Laurens and Constant.  After marrying Laura JOHNSON, a fellow student at Nottingham in 1903, the couple lived mainly in Staithes, but also made several trips to Holland, where Harold became interested in the farming subjects and interiors of simple peasant living, handling these in the manner of the HAGUE SCHOOL of artists.

Harold and Laura KNIGHT moved to Lamorna, Cornwall and lived at Oakhill from 1907-18. There he continued to paint genre subjects, but with a lighter palette, and also painted a number of sitters in Cornwall, including Mornie KERR, Blote Munnings (Florence CARTER-WOOD), and Ella Louise NAPER, the latter for whom he cared deeply.

In 1910 he sold his first painting at NAG, Prayer, and in 1914 he exhibited for the first time at the Paris Salon (Un bohemien).

World War I proved to be a divisive time for the Lamorna community. Harold was a conscientious objector and made his views clear. His health was not good and initially his age precluded him from active service. But in spring of 1918 the conscription age was lowered. When he was called up, he appeared before the West Penwith Tribunal and was exempted from duty on condition that he should carry out agricultural work, which he did, until he was released in the spring of 1919. The experience took his toll on his health and the couple decided that they could no longer endure the hostility from some of their friends and neighbours, and so moved to London to further their careers.

In the capital he continued as a portrait painter of the well-known figures in society and politics of the period, and in 1925 received a Silver Medal for his portrait of Ethel Bartlett at the Paris Salons. The couple were to become the first husband and wife members of the RA in the history of the Academy. Harold pre-deceased Laura by some nine years.