John Kimber is sometimes described as a Bristol captain, but strictly speaking he was the captain of a Bristol ship, the Recovery, owned by the merchant James Rogers and three others. He hailed from Bideford, a north Devonshire port which had seen better times. In the 1680s Bideford was a leading port in the cod fishery of Newfoundland and the tobacco trade of the Chesapeake. By the time Kimber was born, in 1751, it had lost ground to Poole and Glasgow. When Kimber took to the sea at the age of fifteen, Bideford was considered a ‘decayed town’. Trade to foreign parts had declined at the turn of the century, from almost 6,300 tons in 1701 to 2,220 in 1751, falling below 2,000 tons after 1755. The port's main commerce was now coastal, transporting coal from South Wales to local industries, and shipping wheat to regional centres like Bristol.

It was predictable that a boy with maritime ambitions might gravitate to Bristol, unless he was interested in the Royal Navy in which Devonshire men played a conspicuous role. Kimber first appears in the Bristol muster rolls as a seaman on the Brickdale, a brig that made a five-month voyage to Virginia and back in 1772. He is listed there as previously sailing on the Polly, although which Polly is unclear. He made another trip to Virginia on the Caesar in 1774, and then, in what was likely his first slaving trip, as the first mate of the Sally, a schooner bound for Africa and Antigua in May 1775 under the command of James Hodnett. He was 23 years of age. What happened to the Sally is a mystery. It lingered on the Slave Coast for a long time. The muster roll reveals it only reached Antigua in April 1777, nearly two years after its departure from Bristol, before moving on to Montserrat. Four seamen lost patience with the captain in African waters and switched boats; so eventually did Kimber, who on 24 September 1776 entered the Constantine, a larger vessel under the captaincy of Archibald Robe. That ship successfully delivered 600 slaves from the Gold Coast to Grenada after beating off two American privateers during the Middle Passage.