She came from a Christian family and she met Robert Moffat whilst he was a prospective missionary working as a gardener for her father.

[1] Against the advice of the London Missionary Society Robert Moffat set out for southern Africa in 1816.

Soon after she was informed by one of the missionary servants that an infant native baby, whose mother had just died, was customarily buried under some rocks at a nearby hillside.

Her husband Robert, wondering why his wife had not attended services that day, came home to find that Mary had steadfastly adopted the child.

[2] She and Robert were credited with creating a family of "Moffats" who carried forward the mission work.

[3] In 1859 her son John Smith Moffat began working at the mission at Inyathi where he would stay for six years.

[dubious – discuss][5] Moffat was held by the British as the ideal woman Protestant evangelist.

Her correspondence with people in Britain helped to foster support for the work and the letters are now an important record of life in the interior of Africa.