Burns lived in Salford, near Manchester, England. She met Engels during his first stay in Manchester, probably early 1843. It is likely that Burns guided Engels through the region, showing him the worst districts of Salford and Manchester for his research. 
Mary Burns was the daughter of Michael Burns or Byrne, a dyer in a cotton mill, and of Mary Conroy. The family may have lived off Deansgate. She had a younger sister named Lydia (1827–1878), known as “Lizzie," and a niece named Mary Ellen Burns (born 1859), known as "Pumps".
After meeting in the 1840s, Burns and Engels formed a relationship that lasted until Burns' death at the age of 41 on 7 January 1863. Although the custom of the day was marriage, the two were politically opposed to the bourgeois institution of marriage and never married.
Not much is written about Mary Burns. The only direct references to Mary Burns that survived, is a letter from Marx to Engels on learning of her death saying she was "very good natured" and "witty", and a letter from Marx's daughter, Eleanor, saying she was "very pretty, witty and an altogether charming girl, but in later years drank to excess."
- Roy Whitfield: Die Wohnorte Friedrich Engels' in Manchester von 1850–1869 (Where Friedrich Engels live in Manchester). In: Nachrichen aus dem Engels-Haus 3, Wuppertal 1980, p. 85–101
- Roy Whitfield: Friedrich Engels in Manchester, Manchester 1988
- Letter from Engels to Marx, see footnote 179 (page 238) in The Life of Friedrich Engels (volume I) by William Otto Henderson, 1976, ISBN 0-7146-4002-6, read on .)
- year of birth 1823: stated in "Friedrich Engels in Manchester", Roy Whitfield, 1988
- "Friedrich Engels in Manchester", Roy Whitfield, 1988
- Salford Star issue 6 Winter 2007, read on http://www.salfordstar.com/article.asp?id=461