Katherine was born into a wealthy Quaker family in Darlington. She graduated from Somerville Hall (now Somerville College), with Honours in Modern History in 1895, and for a while taught courses through the Extension Division and at Darlington Training College. After the second Boer war, she travelled to South Africa with a committee to investigate the resettlement of single working women from England. In 1906 she married William Scoresby Routledge. The couple went to live among the Kikuyu people of what was then British East Africa, and in 1910 jointly published a book of their research entitled With A Prehistoric People.

In 1910 the Routledges decided to organize their own expedition to Easter Island/Rapa Nui. They had a state-of-the-art 90 foot long schooner built and named it Mana. They arrived on Easter Island on 29 March 1914, and established two base camps, one in the area of Mataveri and the other at the statue quarry, Rano Raraku and also explored Orongo and Anakena. With the help of a talented islander known as Juan Tepano, Routledge proceeded to interview the natives and catalogue the Moai (giant statues) and their platforms.. They excavated over 30 Moai, visited the tribal elders in their leper colony north of Hanga Roa and recorded various legends and oral histories..

One of Katherine’s discoveries was the cultural continuity between the statue carvers and the Polynesian Rapa Nui resident on the island in her time; the designs carved on the back of the statues she excavated included the same designs tattooed on the backs and posteriors of elderly islanders in the leper colony. As the tattooing tradition had been suppressed by missionaries in the 1860s this particular primary evidence was unavailable to later expeditions except through her records.

The Routledges left the island in August 1915 returning home via Pitcairn and San Francisco. Katherine published her findings in a popular travel book, The Mystery of Easter Island, in 1919. Hundreds of the objects that she and her husband found are now in the Pitt Rivers Museum, while her paper records are held by the Royal Geographical Society in London. Most of her scientific conclusions are accepted to this day.

From early childhood, Routledge had suffered from what is today believed to have been the developing stages of paranoid schizophrenia. She had auditory hallucinations and "heard voices." After 1925, her schizophrenia got worse and displayed itself in the form of delusional paranoia. She threw Scoresby out of her Hyde Park mansion and locked herself inside. She also hid many of her field notes. In 1929 Scoresby and her family had Katherine kidnapped and confined to a mental institution, where she died in 1935..