Beardsley was born in Brighton on 21 August 1872. His father, Vincent Paul Beardsley (1839–1909), was the son of a tradesman; Vincent had no trade himself, however, and instead relied on a private income from an inheritance that he received from his maternal grandfather when he was twenty-one.Vincent's wife, Ellen Agnus Pitt (1846–1932), was the daughter of Surgeon-Major William Pitt of the Indian Army. The Pitts were a well-established and respected family in Brighton, and it is widely accepted that Beardsley's mother married beneath her station. Shortly after their wedding, Vincent was obliged to sell some of his property in order to settle a claim for "breach of promise" from another woman who claimed that he had undertaken to marry her.At the time of his birth, Beardsley's family, which included his sister Mabel who was one year older, were living in Ellen's familial home at 12 Buckingham Road.
In 1883 his family settled in London, and in the following year he appeared in public as an "infant musical phenomenon," playing at several concerts with his sister. He attended Brighton, Hove and Sussex Grammar School in 1884, before moving on to attend Bristol Grammar School, where in 1885 he wrote a play, which he performed together with other students. At about the same time his first drawings and cartoons were published in the school newspaper of the Bristol Grammar School Past and Present. In 1888 he obtained a post in an architect's office, and afterwards one in the Guardian Life and Fire Insurance Company. In 1891, under the advice of Sir Edward Burne-Jones and Pierre Puvis de Chavannes, he took up art as a profession. In 1892 he attended the classes at the Westminster School of Art, then under Professor Fred Brown.