Painter, printmaker, and graphic artist Leonard Russell Squirrell was born in Ipswich, England, in 1893. His parents, recognizing his interest and skill in drawing, enrolled him in the Ipswich School of Art in 1908, where he studied under George Rushton. During this time, at age seventeen, he joined the Ipswich Art Club, with whom he would remain a member throughout his life. In 1913 he participated in his first exhibition, entering a watercolor at the Royal Academy and winning the British Institution Scholarship; in 1915, he won the award once again, for an engraving, which hung at the Royal Academy for forty-seven years.

After graduation in 1916, Squirrell enrolled in courses at the Slade School of Art where he studied painting under Philip Wilson Steer and drawing and graphic arts under Henry Tonks. This was followed by trips to Europe to study the countrysides of Italy and France, and in 1925 he traveled to the United States to participate in the International Print Makers Exhibition in Los Angeles. There, he won a silver medal in 1923; subsquent trips won him a second silver medal in etching in 1925 and a gold in 1930. By then he had settled in Ipswich permanently and started a family. He took a position as a printmaking professor at the Ipswich School of Art after the retirement of Charles Edward Baskett in 1929, where he remained until 1940.

In addition to his membership in the Ipswich Art Club, Squirrell became a councilmember of the Royal Society of Painters in Watercolors and the Royal Society of Painter-Etchers and Engravers. Though he occasionally worked in oil paints, his preferred mediums were watercolor, printmaking, and pastel, and he was also a commercial artist, creating posters and ads for companies such as Rolls Royce and posters for the former Great Eastern Railway. He published two books on art techniques, Landscape Painting in Pastel (1938) and Practice in Watercolour (1950). 

Squirrell died in 1979. His exemplary standing as an Ipswich artist earned him a Blue Plaque on the house where he was born.

Among other places, Squirrell exhibited at the Abbey Gallery; Connell & Sons Gallery; Fine Art Society; Glasgow Institute of the Fine Arts; Walker Art Gallery, Liverpool; Manchester City Art Gallery; New English Art Club; Royal Society of Painter-Etchers and Engravers; Royal Hibernian Academy; Royal Institute of Painters in Water Colour and the Royal Scottish Academy.