Pitted against aged customs, superstitions and the hold of witchdoctors on everyday affairs, Slessor, who left Scotland aged just 28, was to ultimately win the respect of tribal elders for her care of the young and her dedication to the remote settlements around Calabar in southern Nigeria.
As she absorbed herself in work, Slessor shed the stiff Victorian clothing of the 19th Century missionary, cut short her red hair and eat the local food, shunning expensive parcels of provisions from back home. She learnt the language, ditching her translator as soon as she could.
But some things were harder for Slessor to acquaint herself with, particularly the belief systems that led to barbarism on a sickening level.
The treatment of newborn twins was to particularly appal this young missionary from the North East.
Twins were routinely killed at birth given the superstition that one of them was the devil, with mothers ostracized from their communities with no means to survive.
Slessor turned to rescuing twins and supporting their mothers - as well as working to change culture and beliefs surrounding the babies.
Against the advice of her mission society, nine twins were adopted by Slessor, known as Ma’ to the children.
A letter from one of her adopted sons Dan, held by the Mary Slessor Foundation, based in Dundee, makes clear the level of love and care she afforded the young ones.
It said: “Ma was the ideal mother, with us she was not the mistress or the missionary worker, she was our mother and the home our family.
“She would bake the family bread but almost all of it goes to the children.
“When one is ill, up she carries him on her bed, well tucked, and then she is busy to prepare some barley broth barefooted, thinly clothes. She would move silently lest she would wake the sick child.”
Having started in the well established mission at Duke Town, Slessor was to become the only missionary working in the remote areas of the Calabar region, which were only accessible by canoe. First she settled in Old Town and then moved deeper, through swampland and junlge, into the territories of the Okoyong tribe.
Slessor was the first outsider ever allowed to live there with the chief welcoming her onto his land and allowing her to build a school.
Witchdoctors were to wield unflinching influence over the communities she serve, with the figures typically administering justice at tribal courts.
Poisonous eser beans were fed to suspects to determine those who were guilty of crimes and offences against the community. Those who vomited up the bean potion were considered innocent, those who died after ingesting it were not.
Slessor increasingly intervened in disputes in order to prevent needless death of innocent people and slowly worked up respect as a result. There are reports of her breaking up fights between tribe members and urging men to sit down beneath trees to talk, while she listened and knitted,
When Southern Nigeria became a British Protectorate, Slessor became the first ever female Magistrate in the British Empire and a skilful diplomatic emissary, known for her able but sometime unconventional judgements.
Slessor died in 1915, aged 67, having suffered long bouts of fever throughout her working life.
She was given a state funeral and is buried at the Eyamba Street Cemetery in Duke Town.
Today, the Mary Slessor Foundation runs social, economic and health care projects in the same area the missionary landed more than 160 years ago.
It was set up by Dr Lawrie Mitchell MBE and his wife Mrs Eme Mitchell, great great granddaughter of Ma Eme, who knew Mary Slessor.
Slessor has appeared on the Clydesdale Bank’s £10 note since 1997.