He became a fluent Irish speaker, and Gaelic League member. As a Sinn Féin activist, he used the name Robiard Ó Flionn/Roibeard Ua Flionn. He married the writer Sylvia Dryhurst on 21 April 1909. They met at Gaelic League meetings in London. Their daughters Máire and Sigle became close friends of Isaiah Berlin. Sigle's son, born in 1941, is artist Tim Wheeler. In March 1924, Robert and Sylvia moved to what was to be their long-term married home, the elegant Regency house of 5 Keats Grove in the leafy suburb of Hampstead, north-west London. The house had been lived in by various members of Sylvia's (Dryhurst) family. James Joyce and his wife Nora Barnacle held their wedding lunch at the Lynds’ house after getting married at Hampstead Town Hall on 4 July 1931. Lynd died in Hampstead in 1949. He is buried in Belfast City Cemetery.