Deck was born in Sydney, Australia on 29 May 1882 to Dr John Feild Deck and Emily (née Young, elder sister of missionary
Florence Young). Deck's grandfather was evangelist
James George Deck, who had emigrated from England to New Zealand with his family, including his son John Feild Deck, in 1853. John Feild Deck and Emily Baring Young married in New Zealand in 1865, and in 1877 moved from New Zealand to Australia with their family, settling in Sydney. Four of John and Emily's sons became doctors, and seven of their eleven children became missionaries: five with the
South Sea Evangelical Mission (SSEM) and two with other missions. Deck graduated from
Sydney University in 1906 as a Bachelor of Dentistry and began practising in
Cowra, New South Wales. During 1909 Deck returned to Sydney to begin a practice with his brother. ==Missionary work==