He was born on Spike Island, County Cork, Ireland on 29 April 1826, the son of James Cain (1797–1871), a private soldier in the 88th Foot, a regiment of the British Army.
However, according to Routledge, Robert Cain was born in poverty in 1826, the son of a private soldier who would soon be forced to leave the army and travel to England to find work.
Cain arrived in Liverpool with his parents in late 1827 or early 1828 and grew up in the slums of the Islington area of the city with his older sister Hannah and two younger siblings, Mary and William.
At the same time as he was developing his brewing business, Cain also made shrewd property deals and ran a hotel near to the brewery on Stanhope Street; as the company grew it expanded by buying out smaller brewers and taking control of their pubs.
From the early 1860s the Cains lived in the affluent enclave of Grassendale Park and later owned mansions on Aigburth Road and in Hoylake on the Wirral.