William Lever was born on 19 September 1851 at 16 Wood Street, Bolton, Lancashire, England. He was the eldest son and the seventh child born to James Lever (1809–1897), a grocer, and Eliza Hesketh, daughter of a cotton mill manager. From age six to age nine William attended a small private school run by the Misses Aspinwall in a house on Wood Street, not far from the Lever family home. At the age of nine, he was sent to another of Bolton's private schools before finishing his formal education at Bolton Church Institute from 1864 to 1867. Not a particularly bright scholar, he was nevertheless keen to acquire academic learning. His mother wanted him to enter the learned professions, ostensibly medicine, and William himself was very interested in becoming an architect. His father, however, had other, somewhat less erudite plans for his eldest son, and thus, not long after his fifteenth birthday, he started to work in the family grocery business. By then, the Lever family had moved from Wood Street to a larger house adjacent to the grocery business. In the celebrated Victorian manner, the boss's son was, initially at least, shown no preferential treatment, being required to sweep the floor and tidy up before the staff arrived. Other tasks included various practical assignments more to do with the fundamentals of the wholesale grocery trade, almost certainly designed to prepare the youth for management in later years. His remuneration was "a shilling a week all found" which meant that his board and lodgings were provided, making the financial aspect of the contract more-or-less pocket money.

At some stage, William was moved to the administration department where he learned about and subsequently reorganised the firm's accounting and bookkeeping systems. Perhaps in order to escape the shackles of his father's close supervision, he eventually petitioned to take the place of a retiring sales representative; in those days, being a "rep" meant a great deal of travelling by horse and carriage and spending nights away from home, as well as a measure of independence and some leeway in making decisions and brokering deals with the canny retailers on his route.

The Lever family were Congregationalists and James Lever, a teetotaller and a non-smoker, applied its principles in his business life as well as in his personal life. In accordance with nonconformist tenets, the Lever family held frequent bible readings at home, and were regular worshipers at the local chapel. Thus, William's circle of friends tended to comprise children of similar backgrounds and beliefs. Among these was Elizabeth Ellen Hulme (Dec 1850 – 24 July 1913) whose family also resided on Wood Street. In the tradition of the nineteenth-century well-to-do middle classes, William paid court to Elizabeth over several years and, when the financial circumstances allowed, he formally proposed marriage. On 17 April 1874, after a two-year engagement, they were married at the Church of St Andrew and St George (then Congregational, now United Reformed) on St Georges Road, Bolton.

In 1879 the Lever family business acquired a failing wholesale grocer in Wigan, affording young William an opportunity to prove his ability as a quasi-autonomous administrator. The expanded activity necessitated a search for new suppliers, taking William to Ireland, France and other parts of Europe, appointing local agents to safeguard the firm's interests. At this time, his flair for advertising and branding began to emerge as he successfully differentiated the Lever brand from generic commodities. By the end of 1879, the business' prospects were good enough to convince William and Elizabeth to invest in a new home in Bolton and by 1881 the expanding Wigan business warranted the commissioning of new premises; Lever and Company was expanding steadily.