Previously in the private collection of Leach's son David, the 16½in (42cm) dish with a trailed 'well head' design, signed and dated BL 1929 to the base, was acquired from him in the late 1990s by his close friend Andy Christian, the first director of The Devon Guild of Craftsmen.
It was sold by Maak, the London-based specialists in contemporary ceramics, on May 17 for £12,000 (£14,400 including premium).
Stephanie Murfin, curator of decorative art at the Harris, described it as an important purchase for the museum, who had been looking to build on their existing collection for some time.
"On his return to the UK from Japan in 1920, Leach heralded a new chapter in British ceramic history - one that [our] existing collection did not explore until now. Our aim in acquiring an example of Leach's work is to secure a piece that best encapsulates the artist's early spirit of experimentation and his distinctive philosophy, one based on fusing the cultures of East and West, promoting the value of hand over machine production, and the importance of ceramic practice as a unified creative and technical endeavour."