Margaret Cathcart was born in Northampton County, North Carolina on August 18, 1754. The daughter of a prominent doctor, Margaret and her siblings were had educational opportunities that were uncommon for young North Carolinian women of their time. Margaret's father brought Daniel Earle, a noted religious figure, from England to the colony to tutor the Cathcart children.

In 1774 Margaret and her sister Frances became two of the fifty-one signers of a women's nonimportation agreement which later became known as Edenton Tea Party Resolves. The following year she married Reverend William Bryan McKenzie. She died in North Carolina on October 11, 1823.