Booth was born in Sneinton, Nottingham, England, the only son of four surviving children born to Samuel Booth and Mary Moss. His father was wealthy by the standards of the time, but during Booth's childhood, as a result of his father's bad investments, the family descended into poverty.
In 1842, Samuel Booth, who by then was bankrupt, could no longer afford his son's school fees, and 13-year-old William Booth was apprenticed to a pawn-broker. Samuel Booth died later that same year.
Two years into his apprenticeship Booth was converted to 'salvation' and Methodism. He then read extensively and trained himself in writing and in speech, becoming a Methodist lay preacher. Booth was encouraged to be an evangelist primarily through his best friend, Will Sansom. Sansom and Booth both began in the 1840s to preach to the poor and the "sinners" of Nottingham, and Booth would probably have remained as Sansom's partner in his new "Mission" ministry, as Sansom titled it, had Sansom not died of tuberculosis, in 1848.