Mary Helen Agnes Allies (2 February 1852 – 27 January 1927) was a Catholic historian, writer and translator.

The family moved to Portman Square and Mary boarded at Holy Child College, a Catholic school in St Leonards-on-Sea operated by the Society of the Holy Child Jesus (later merged into their Mayfield school), and subsequently the Visitation Convent Paris.

Allies gave a lot of respect to her father and in time she would write his biography.

This, and the shorter version published in 1897,[3] as of 2004 was the only available biography of Pius VII in English and is therefore considered a standard work.

[4] Her next work, Three Catholic Reformers (1876) was considered too pious and uncritical of her subjects[citation needed].