He was born in
Schull,
County Cork, Ireland, the son of James Sampson (1813-c. 1871), a chemist and engineer, and his wife Sarah Anne Macdermott; he was brother to
Ralph Allen Sampson (1866-1939). James Sampson left Ireland after losing all his money in a bank failure. The family with four sons moved to
Liverpool in 1871. John Sampson, the eldest, left school at the age of 14, after his father's death, and was apprenticed to the engraver and lithographer Alexander MacGregor. MacGregor retired when Sampson was aged 22, and from 1888 he ran his own printing business, in Liverpool's Corn Exchange. Sampson became librarian at
University College, Liverpool in 1892, largely self-taught. His printing business had failed that year, and his application was supported by
Kuno Meyer. In 1894, on a camping trip with others from the College, he encountered the musician Edward Wood, near
Bala. The Wood family to which he belonged, descendants of
Abram Wood (died 1799), were noted as speakers of Welsh-Romani, a quite pure inflected Romani dialect, which was to become Sampson's major study, and which earned him the sobriquet
Romano rai ("Romany Lord", Gypsy scholar), or just "the Rai". They were also musicians, twenty-six harpists being noted from the 18th century. In 1896, through Lloyd Roberts, a harpist and Edward Wood's brother-in-law, Sampson found Matthew Wood, on
Cader Idris, who moved shortly to
Abergynolwyn. He was brother to Edward, and with his four sons more fluent in Welsh Romani, in which they told folk tales. Sampson spent vacations with them, and began a thirty-year lexicographical and philological project on the language. Matthew Wood, however, abruptly disappeared some three years later. In 1901 Sampson met the artist
Augustus John, who was teaching in an art school connected with University College. They struck up a long friendship, leading to an emphasis in John's works on
Romani subjects. At this period Sampson also knew the Polish painter
Albert Lipczyński, who was in Liverpool with an introduction to John; Sampson found him an interpreter, "Doonie", who became his wife. ==Researcher with assistants==