William Bernard Ullathorne OSB (7 May 1806 – 21 March 1889) was an English prelate who held high offices in the Roman Catholic Church during the nineteenth century.

Ullathorne was born in Pocklington, East Riding of Yorkshire, the eldest of ten children of William Ullathorne, a prosperous businessman with interests in groceries, draperies and spirits, and Hannah (née Longstaff), who converted to Roman Catholicism when she married.

While attending Mass in Memel he experienced something in the nature of a conversion, and on his return asked the mate if he had any religious books.

Ullathorne was given a translation of Marsollier's Life of St Jane Frances de Chantal, which deepened his religious devotion.

In February 1823, aged 16, he was sent to Downside School, near Bath, where he was mentored by John Bede Polding, afterwards the first Archbishop of Sydney, who influenced him greatly.

He was ordained priest in 1831, and in 1832 went to New South Wales as vicar-general to Bishop William Placid Morris (1794–1872), whose jurisdiction extended over the Australian missions.