James Deemin was born on 4 May 1863, at Berkeswell, near Meriden, Warwickshire. Little is known of his background, except that his father, William Deemin, was a farmer, and that his mother's maiden name was Astley. Family tradition suggests that James Deemin left school at an early age and obtained employment in a Coventry cycle works. He is said to have been ambitious as a child and, finding that prospects of advancement were extremely limited at home, determined to try his luck abroad. In 1882, at the age of 19, James Deemin travelled to Liverpool and began his career as a West African merchant, working for John Holt and Company.

James Deemin spent his entire business career with John Holt's. From 1883 to 1914, he was a vital part of their Coast staff, eventually becoming Agent-General for the Company. Eight of these years were utilised in fighting Holt's case against the 'concessionaire' policy of the French Government at Libreville, an activity that eventually resulted in substantial compensation. In 1914, Deemin was captured by the Germans in the Cameroons (Republic of Cameroon). His captivity did not last long and he was rescued by the Royal Navy and subsequently repatriated to England. By then, the effects of long exposure to a severe tropical climate, together with the shock of imprisonment, had weakened his health and he was taken to a nursing home in Gambier Terrace, Liverpool. Once fully fit, he left the home and, soon afterwards, married the Assistant Matron; Sister Edith Evans. Deemin was then aged 52 and this was his first and only marriage. From this time onwards, he was subject to frequent attacks of malaria but was nevertheless able to play an active and responsible part in John Holt's Liverpool Office. Deemin retired in 1931 and, from then until his death in Mar 1939, lived quietly in Prenton, Birkenhead.