In December 1909 Leech exhibited with Jack Yeats, Albert Power, Eva Hamilton, William Orpen, Lily Williams, A.E., Constance Gore-Booth and Dermod O’Brien in the first Aonach art exhibition, organised by Sinn Féin as part of the Irish Festival at the Rotunda.
On his return to France he met and in 1912 married Saurin Elizabeth née Smith (1879–c1951)[1], a young painter of a similar style.
Leech would travel throughout Europe and eventually settled in England in 1919, with frequent visits to the South of France, to Marseilles, Grasse and Cagnes-sur-Mer.
In about 1919 William was commissioned by a London solicitor Percy Dumville Botterell CBE (1880–1950) to paint a portrait of his wife May née Pearson (1881–1965).
The works of Leech feature coastal and harbour scenes, landscapes, interiors, still life and portraits.