Ullathorne was born in Pocklington, East Yorkshire, the eldest of ten children of William Ullathorne, a prosperous businessman with interests in groceries, draperies and spirits, and Hannah, who converted to Roman Catholicism when she married. When he was nine years of age, Ullathorne's family relocated to Scarborough, where he began his schooling. He was a descendant of Saint Thomas More through his great-grandmother, Mary More. At 12 he was taken from school and placed in his father's office to learn the management of accounts. The intention was to send him to school again, but Ullathorne wished to go to sea, and at the age of 15, with his parents' permission, he made the first of several voyages to the Baltic Sea and Mediterranean. 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. At the end of this voyage he returned home. 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.
Priesthood
In 1823 Ullathorne entered the monastery of Downside Abbey, taking the vows in 1825, taking the additional name "Bernard", after Bernard of Clairvaux. He was ordained priest in 1831, and in 1832 went to New South Wales as vicar-general to BishopWilliam Placid Morris, whose jurisdiction extended over the Australian missions. It was mainly Ullathorne who caused Pope Gregory XVI to establish the hierarchy in Australia. In 1836, Bede Polding sent Ullathorne back to Britain, to recruit more Benedictines. While in England, he visited Ireland, where he met Mary Aikenhead. He returned to Australia in 1838 with five Sisters of Charity. Ullathorne returned to England in 1841, suffering what Judith F Champ says would in modern terminology be described as "burnout". He then took charge of the Roman Catholic mission at Coventry, where he recovered his health and spirits. Ullathorne had turned down bishoprics in Hobart, Adelaide, and Perth as he did not wish to return to Australia, but in 1847 he was consecrated bishop as Vicar Apostolic of the Western District, in succession to Bishop C.M. Baggs, but was transferred to the Central District in the following year. Ullathorne helped found St Osburg's Church in Coventry.