Mather was the founder of the Royal National Mission to Deep Sea Fishermen (1882) which provided 'sailing hospitals' for the North Sea fishing fleet and campaigned against 'cooperage', the system of traffic in spirituous liquors, tobacco and other articles among the fishing boats. He wrote Nor'ard of the Dogger, or, Deep Sea Trials and Gospel Triumphs : Being the Story of the Initiation, Struggles, and Successes of the Mission to Deep Sea Fishermen (London, 1887), a history of the MDSF, in an attempt to increase public support for it. After being criticised for financial irregularities and being forced to resign from the MDSF he left for Australia in January 1890, living here for two years and researching for his book The Squatter's Bairn. He later anonymously published his autobiography, Memories of Christian Service (1922).