Julia Diana Dickson, called in religion Mary Bernard, was born at Ipswich, Suffolk, England, probably in 1810 or 1811, daughter of Richard Lothian Dickson and his wife, Julia Dickson. An adult convert to Catholicism, she was baptised and confirmed at Edinburgh on 24 May 1845, and on 1 May 1847 entered the Bermondsey convent of the Sisters of Mercy in London. After making her act of profession on 11 February 1850, she moved to the Chelsea convent and during the next four years acquired nursing experience at St George's Hospital, London.
Five nuns from Bermondsey convent were among the 40 women taken by Florence Nightingale to nurse troops in the Crimea; they arrived at Scutari on 3 November 1854. A second group including 14 Irish Sisters of Mercy landed at Constantinople on 15 December. Sister Mary Bernard, the sole Bermondsey sister in this party, was one of five nuns assigned to work under Florence Nightingale at the General Hospital, Scutari. Before long she contracted severe fever, so serious that twice she received the last rites. In July 1855 she was invalided home, where she made a complete recovery.
In 1857 she set out with five other sisters to join the Auckland community of the Sisters of Mercy, arriving in New Zealand on the Dinapore on 5 August 1857. She described her first impressions of Auckland in a letter written soon after her arrival: 'We walked up what I suppose is called the principal street, which has a curious straggling appearance, with wooden houses, looking rather like enlarged bathing machines.' If the town seemed untidy and makeshift, Sister Mary Bernard was optimistic: 'as everything grows very quickly in this lovely climate, in a few years the Convent will be one of the prettiest in the view of the approach to Auckland.' She concluded, 'there is so much to be done, and I am so grateful to Almighty God for giving me the grace to come so far, and leave all I loved so dearly to work in this distant land.'
At first the Sisters of Mercy in Auckland were engaged in educational and social work, rather than nursing. Consequently Sister Mary Bernard became a teacher at the boarding school for young ladies established by the St Patrick's community. During 1861 Bishop P. J. Viard, who had been struggling to establish a Marist convent in Wellington, appealed to Bishop J. B. F. Pompallier for support. As a result Sister Mary Bernard and two other sisters were sent to Wellington, arriving on 14 June 1861 on the Lord Worsley. Mary Bernard became the first superior of a community of the Sisters of Mercy outside Auckland. In his instructions to Mother Mary Bernard, Bishop Viard emphasised that the convent must be self-supporting. This task was daunting, but the sisters soon received support for their work. For the next 13 years Mother Mary Bernard Dickson (known in the Wellington diocese as Dixon) taught at the convent school, and helped to lay a solid foundation for the education of girls in Wellington.
In May 1874 the Melbourne Sisters of Mercy took responsibility for the Wellington convent. Mary Bernard was now free to return to Auckland; instead she accepted an invitation from Father Eugene Pertuis to found a community at Ahaura, on the West Coast goldfields. On 1 July an advertisement appeared in the Grey River Argus announcing the establishment of a boarding and day school for young ladies by the Sisters of Mercy, and setting out the fees. But by the end of 1874 the parish was heavily in debt and Father Pertuis was recalled to Wellington. He blamed the Sisters of Mercy for 'having too many children to keep and some not paying regularly.' Although the venture failed, the sisters had broken new ground in founding the first community of Catholic nuns in the South Island.
Mother Mary Bernard eventually returned to Auckland and died there on 5 August 1895. While her achievements in New Zealand were notable, it was for her earlier nursing experience that she was honoured after her death. During his term of office the governor general, Lord Bledisloe, went every year to Mother Mary Bernard's grave at the Ponsonby convent to lay a wreath in recognition of her services at the Crimea.