Kallenbach was introduced to the young Mohandas Gandhi while they were both working in South Africa and, after a series of discussions, they developed a long-lasting association.

A skilled ice-skater, swimmer, cyclist, and gymnast, and successful architect, Kallenbach acquired considerable property in South Africa.

[4] On this farm, Kallenbach abandoned the life of a wealthy, sport-loving bachelor, adopting the simple lifestyle, vegetarian diet and equality politics of Gandhi.

Also, Kallenbach acted as a manager during Gandhi's 1907–13 satyagraha movement in South Africa culminating in the 1913 Epic March.

[9] At the request of Moshe Shertok (Sharett), Kallenbach visited Gandhi in May 1937 to enlist his sympathy and support for Zionism.

His large collection of books went to the Hebrew University of Jerusalem, and his cremated remains were buried at Kibbutz Degania in Israel.

[1] Kallenbach was one of the foremost associates and friends of Gandhi, devoting a major part of his life to following his principles and ideals.

Gandhi has frequently mentioned him in his autobiography, where he explains how Kallenbach was his 'soulmate'[10] in the early days of the development of his personality and ideology.

In his book, Great Soul: Mahatma Gandhi and His Struggle With India, Joseph Lelyveld quotes Tridip Suhrud, a cultural historian, as claiming: "They were a couple."

[12] The Indian government' has stated that the purchase of the private correspondence of their cultural and socio-philosophical leader was to prevent it from being auctioned for profit.