Kingsley was born in Islington, London on October 14, 1862. She was the daughter and oldest child of traveler and writer George Kingsley and Mary Bailey, and was the niece of novelists Charles Kingsley and Henry Kingsley. Mary's parents married just 4 days before her birth, a fact which she kept very private. The family moved to Highgate less than a year after her birth, the same home where her brother Charley was born in 1866. Her father was a doctor and worked for George Herbert, 13th Earl of Pembroke and other aristocrats, often away from home on his excursions. During these voyages he was able to collect information for his studies. Dr. Kingsley and Lord Dunraven ventured to North America between 1870 and 1875 and was offered the opportunity to join American General Custer and his men into Native American lands. Later reports describing the massacre of Custer's party left the Kingsley family terrified, but they were relieved to discover later that bad weather had kept Dr. Kingsley from joining the Custer party. It is likely that her father's views on the injustices faced by the Native Americans helped shape Mary's later opinions on British imperialism in West Africa.

Mary was not baptized nor and was brought up as a Christian. She had little formal schooling other than German lessons at a young age, but she did have access to her father's large library and loved to hear her father's stories of foreign countries. She did not enjoy novels that were deemed more appropriate for young ladies of the time, such as those by Jane Austen or Charlotte Bronte but preferred books on the sciences and memoirs of explorers. Charley, however, was sent to school and entered Christ's College in 1886 with the intent to become a lawyer, allowing Mary the chance to make several academic connections and a few friends.

In her later years, Mary's mother became ill and Mary was expected to care for her well-being. Mary was unable to leave her mother's side for more than a few hours and therefore had limited travel opportunities. Her father also became bedridden with rheumatic fever after an excursion. Dr. Kingsley died in February 1892 and Mrs. Kingsley followed a few months later in April of the same year. Freed from her family responsibilities and with an inheritance of £8,600 to be split evenly with her brother, Mary was now able to travel as she dreamed. Mary decided to visit Africa to collect the material she would need to finish off a book that her father had started on the culture of the people of Africa.

After a preliminary visit to the Canary Islands, Mary made preparations to travel to the west coast of Africa. The only non-African women who dared brave the dangers of Africa were usually the wives of missionaries, government officials, or explorers, a stereotype which she struggled to overcome throughout her lifetime. Exploration and adventure were not seen as fitting roles for a Victorian woman. Even African tribal women were astonished that a woman of Mary's age was traveling without a man, as she was frequently asked why her husband was not accompanying her.

Mary landed in Sierra Leone on August 17, 1893 and pressed on into Luanda in Angola . She lived with local people who taught her necessary skills for surviving in the African jungles, and often went into dangerous areas alone. Her training as a nurse at the Kaiserworth Medical Institute prepared her for slight injuries and jungle maladies that she would later encounter. Mary returned to England in December 1893.

Upon her return, Mary secured support and aid from Dr. Albert Gunther, a prominent zoologist at the British Museum, as well as a writing agreement with publisher George Macmillan for she wished to publish her travel accounts.

She returned to Africa yet again in December 1894 with more support and supplies, as well as increased self assurance in her work. She longed to study cannibal tribes and their traditional religious practices, commonly referred to as fetish during the Victorian Era. In April she became acquainted with Scottish missionary Mary Slessor, another female living amongst the natives with little company and no husband. It was during her meeting with Slessor that Kingsley first became painfully aware of the tribal custom of twin killing, a custom Slessor was determined to stop. The native people believed that one of the twins was the offspring of the devil who had secretly mated with the mother and since the innocent child was impossible to distinguish, both were killed and the mother was often killed as well for somehow attracting the devil to impregnate her. Kingsley arrived at Slessor's residence shortly after she had taken in a recent mother of twins and her surviving child.

Later while in Gabon, Mary Kingsley travelled by canoe up the Ogooué River where she collected specimens of previously unknown fish, three which were later named after her. After meeting the Fang tribe and traveling through uncharted Fang territory, she climbed the daring 13,760 ft Mount Cameroon by a route previously unattempted by any other European.

When she returned home in November 1895 Kingsley was greeted by journalists who were eager to interview her. The reports that were drummed up about her voyage however were most upsetting to Kingsley, as the papers portrayed her as a "New Woman", an image which she did not embrace. Kingsley distanced herself from any feminist movement claims, arguing that she had never worn trousers during her expedition and even denounced equality for women in scholarly societies. She dressed conservatively and tried to avoid any more controversy than her studies already attracted her.

Over the next three years, she toured the country giving lectures about life in Africa to a wide array of audiences. She was the first woman to address the Liverpool and Manchester chambers of commerce.

Mary Kingsley upset the Church of England when she criticized missionaries for attempting to change the people of Africa. She talked about, and indeed defended, many aspects of African life that had shocked many English people, including polygamy. For example explaining the "seething mass of infamy, degradation and destruction going on among the Coast native... [as] the natural consequence of the breaking down of an ordered polygamy into a disordered monogamy". She argued that a "black man is no more an undeveloped white man than a rabbit is an undeveloped hare" as well asserting that she did not regard "the native form as 'low' or 'inferior'... but as a form of mind of a different sort to white men's - a very good form of mind too, in its way." After living with the African people, Kingsley became directly aware how their societies functioned and how prohibiting customs such as polygamy would be detrimental to their way of life. She knew that the typical African wives had too many tasks to manage alone and did not view their marriage situations as cruel or unfair. Missionaries in Africa often required converted men to abandon all but one of their wives, thus leaving the other women and children without the support of a husband. Despite these seemingly radical views on justifying African ways of life, she was fairly conservative on other issues and did not support the women's suffrage movement.

Kingsley wrote two books about her experiences: Travels in West Africa (1897), which was an immediate best-seller, and West African Studies (1899), both which granted her vast respect and prestige within the scholarly community. Some newspapers refused to publish reviews of her works, such as the Times colonial editor Flora Shaw, likely on the grounds that her beliefs countered the imperialistic intentions of the British Empire and the commonly accepted notion that African natives were inferior peoples. It is likely that she refrained from any suffrage connections in order to insure her work was received favorably.

During the Second Boer War, Kingsley traveled to Cape Town and volunteered as a nurse. She was stationed at Simon's Town hospital, where she treated Boer prisoners of war. After contributing her services to the ill for about two months, she developed symptoms of typhoid and died on June 3, 1900. In accordance with her wishes, she was buried at sea.

Kingsley's tales and opinions of life in Africa helped draw attention to British imperial agendas abroad and the native customs of African people that were previously little discussed or misunderstood by the European masses. The Fair Commerce Party formed soon after her death, pressuring for improved conditions for the natives of British colonies. Various reform associations were formed in her honor and helped facilitate governmental change. The Liverpool School of Tropical Medicine founded an honorary medal in her name. Her understanding and empathy for the native African people and their interests, along with her stance on their so called "savage" way of life earned her unwanted fame and a mislabel as a feminist, an image she countered whenever given the chance.

• The Travelling Naturalists by Clare Lloyd. (Study of 18th Century Natural History - Includes Charles Waterton, John Hanning Speke, Henry Seebohm and Mary Kingsley Contains colour and black and white reproductions.
• Blunt, A. Travel, Gender and Imperialism: Mary Kingsley and West Africa, Gilford Press 1994
• Davidson, L.C. Hints to Lady Travellers, London 1889
• Dea, B. Mary Kingsley: Imperial Adventuress, Palgrave Macmillan 1992
• Kingsley, M.H. West African Studies, Frank Cass Publishers 1964
• Kingsley, M.H. 'Travels on the western coast of Equatorial Africa' Scottish Geographical Magazine, 12, p. 113-124, 1896
• Middleton, D. 'Some Victorian Lady Travellers' The Geographical Journal, 139(1), p. 65-75, 1973
• Mcloone, M., Women explorers in Africa: Christina Dodwell, Delia Akeley, Mary Kingsley, Florence von Sass Baker, and Alexandrine Tinne (Capstone Press, 1997)
• 'Kingsley, Mary Henrietta' Oxford Dictionary of National Biography, Oxford University Press 2004
• Bausch, Richard Hello To The Cannibals, HarperCollins, 2002 (fictional approach) Mar kingsley