Leach was born in Hong Kong, the son of English parents (his father in the Colonial service) and the grandson of Christian missionaries. His mother died soon after he was born, and he was sent for some years to live with his grandparents in Japan. He was returned to England at the age of ten for his schooling, and in 1903 entered the Slade where he flourished under the inspired draughtsmanship of Henry TONKS, and later the London School of Art (1906) where he was exposed to the extraordinary etching skills of Frank BRANGWYN. With a small etching press, a small annual income and some important introductions, Leach returned to Japan in 1909, at twenty-two years of age. It was in Japan that he discovered the wealth of art forms and philosophies that influenced the direction of the rest of his life.

Leach's British associations with Augustus Edwin JOHN, Tonks and Brangwyn stood him in good stead as he confidently began to write about etching, mentioning these famous English artists’ names, and introducing that art through demonstrations and lectures. The Japanese, in return, introduced him to pottery, and he began to study under Ogata Kenzan (VI amongst a family line of master potters). With fellow pupil Kenkichi TOMIMOTO, Leach was to inherit the title of Kenzan VII, and to set up his first pottery in Japan. In 1917, at the home of a friend Soetsu YANAGI, he was also to meet the young Shoji HAMADA, who was to remain a life-long friend. After eleven years in China and Japan, Leach returned to England with Shoji Hamada and established the St Ives Pottery in 1920 along Japanese lines. 

This initiative became the ‘starting point of modern ceramics’  (British Studio Ceramics p22). The relative isolation of  St Ives, and the brief length of the summer tourist season, affected the sales of his products, and at one point he was saved from bankruptcy by the Elmhirsts of Dartington. He began to exhibit in London and Japan, and also in Cornwall at the Newlyn Art Gallery from 1924, when crafts became a part of the exhibition programme there. He also exhibited twenty-seven pots with STISA when their 1925 show opened at the Cheltenham Art Gallery.

His etching, Self Scrutiny (1916), was displayed in the Faces of Cornwall (Portraiture) Exhibition at Penlee House, Penzance in 2005, the gift of a patron to Penlee House.