Siddig's mother remained in Sudan for three years and returned to London with Siddig and his father. Siddig was 2 years old at the time. Siddig spoke Arabic when he was young, but is no longer able to speak or understand the language. He told "Bidoun" magazine that, according to his mother, he had forgotten the language within two years of moving to London. In 1978 his mother married film director and producer Michael Birkett and in 1982 the two had a son together named Thomas. Siddig's mother worked as a model and theatrical press agent.