In 1889, in Adelaide, Bragg married Gwendoline Todd, a skilled water-colour painter, and daughter of astronomer, meteorologist and electrical engineer Sir Charles Todd. They had three children, a daughter, Gwendolen and two sons, William Lawrence, born in 1890 in North Adelaide, and Robert. Gwendolen married the English architect Alban Caroe, Bragg taught William at the University of Adelaide, and Robert was killed in the Battle of Gallipoli. Bragg's wife, Gwendoline, died in 1929.