Born in Brighton, Gill was the son of a Church of England clergyman. He studied at the Chichester Art School and in 1900 was briefly apprenticed to an architect in London. He then resumed his studies of art and typography at the Central School of Arts and Crafts and studied the craft of carving inscriptions at Westminster Technical Institute. He was a member of the Art Workers' Guild and of the Fabian Society. He began to earn his living as a letter cutter in 1903, began to carve figures in 1910 and exhibited at the Chenil Gallery in 1911. In 1913 he became a convert to Roman Catholicism and was commissioned to make the Stations of the Cross at Westminster Cathedral, 14 relief carvings which he did in 1914-18. These and the Prospero and Ariel group on Broadcasting House (1929-31) are his best-known carvings. Having been commissioned to do a group of Prospero and Ariel, he made in fact a sculpture of God the Father and God the Son, with the Son (Ariel) bearing the stigmata. He wrote: 'I took it upon me to portray God the Father and God the Son. For even if that were not Shakespeare's meaning, it ought to be the BBC's.' After the war he became a Tertiary of the Order of St. Dominic and founded a Guild of St. Joseph and St. Dominic, which was to be a guild of craftsmen with the object of reviving a religious attitude towards art and craftsmanship in opposition to the social and economic trends of the time. In 1924 Gill began his association with the Golden Cockerell Press of Robert Gibbings, for which he illustrated many books. He also designed the 'Perpetua' and 'Gill Sans-serif' typefaces for the Monotype Corporation.
In sculpture Gill was one of the protagonists in the movement for the revival of direct carving. He was also a major figure in the revival of book design and typography. Among the best known of the books he designed and illustrated are The Canterbury Tales (1927) and The Four Gospels (1931). Chief among his own writings were Art (1934), in which he expounded his own views about the nature of art, claiming to 'debunk' the 'bunk' that is written about it and attacking its commercialization, and his Autobiography, written in 1940. In his life, his work and his writing he was a vigorous advocate of a romanticized medievalism. An exhibition at Kettle's Yard, Cambridge, in 1979 and an exhibition at the Whitworth Art Gallery, Manchester University, 1980 demonstrated the lasting interest in his work.