Dr Pfau dedicated her life to treating patients in Pakistan.
Widely known as Pakistan's Mother Teresa, Pfau was eulogised by the prime minister and army chief for her contributions towards freeing the country of a contagious disease that can cause disfigurement.
Here is how people reacted to her demise news on Twitter. "We will remember her for her courage, her loyalty, her service to the eradication of leprosy", Prime Minister Shahid Khaqan Abbasi said in a statement.
Dr Pfau, 87, who was suffering from complications related to old age, had been admitted to the Aga Khan Hospital two weeks ago where her condition was pronounced unstable.
Born in Leipzig, Germany on September 9, 1929, Dr Pfau devoted the last 50 years of life to fighting leprosy in Pakistan. Patients from all over Pakistan and even Afghanistan came for their treatment in Karachi's leprosy center.
With her efforts, in 1996, the World Health Organisation declared Pakistan one of the first countries in Asia to have controlled leprosy.
She studied medicine in Germany in the 1950s and joined the Daughters of the Heart of Mary before leaving for India via Karachi.
In 1963, she founded MALC with the opening of a clinic.
German-Pakistani nun Dr Ruth Pfau died in Karachi on Thursday. The nun persuaded the Pakistani government five years later to start a programme against leprosy across the country. Dr Pfau was also awarded the Hilal-e-Pakistan in 1989 and Hilal-e-Imtiaz in 1979.