[1] He worked professionally in the ship breaking business throughout his life and was an influential breeder of fox terriers.
[5] Professionally, Castle joined Henry Castle and Sons, his father's firm of ship breakers and timber merchants which operated on the River Thames at Baltic Wharf in central London, Woolwich and Charlton.
[5] Castle initially lived at Blackheath, and married Katherine Batho in 1888; the couple had three children.
[2][3][7] Their son, also named Sidney, was killed in the First World War whilst serving as a lieutenant in the 6th battalion of the Middlesex Regiment.
[5] A keen breeder of fox terriers, he was a member of the Fox Terrier Club, and served on its committee for over 30 years, and was a member The Kennel Club in the early 20th century and regularly judged at dog shows.