He was born in 1883 in a respectable family at Howrah, and was known as Khagendranath Mullick in his pre-monastic life. Of a quiet nature he used to be seen meditating in lonely corners even as a boy. After passing out of school, he happened to learn from his close friend Jitendranath (later Swami Vishuddhananda, the eighth President of the Ramakrishna Order) about Sri Ramakrishna. He began frequenting Dakshineswar and other places connected with the Master in the company of his two friends, Jitendranath and Girija, whose acquaintance he made at Sri Ramakrishna Yogodyana, Kankurgachhi.
Imbued with intense dispassion, the three together decided to renounce the world and go out as mendicant monks. They accordingly started out in July 1907 for Puri. On their way, they halted at Jayrambati to have the darshan of Sri Sarada Devi, the Holy Mother, by whom they had previously been initiated. She also gave them the gerua robes and told them to go to Varanasi and stay at the Ramakrishna Advaita Ashrama, where they could get the guidance of Swami Shivananda, one of the direct disciples of the Master. Khagendranath was given the name ‘Santananda’ by Mahapurush Maharaj, and later, in 1921, was formally initiated into sannyasa by Swami Brahmananda.
Given to intense spiritual practices, he spent most of his earlier life at Varanasi, though he frequently went on pilgrimage. He visited almost all the important pilgrimage centres in India.
In 1930 the Swami was appointed a trustee of the Ramakrishna Math and a member of the Governing Body of the Ramakrishna Mission. He was also made the Head of the Ramakrishna Advaita Ashrama, Varanasi; but after a time he resigned the post and engaged himself in the worship at the shrine, which work suited his meditative temperament better.
Swami Santananda had to leave Varanasi in 1949 for treatment of tuberculosis and spent a few years convalescing at the Ramakrishna Mission T. B. Sanatorium, Ranchi. From 1963 he spent the remaining years of his life at Belur Math. He bore calmly and without complaint the physical ailments that attended the last twenty years of his life.
The Swami was highly respected and loved for his spiritual attainments and sweet nature. His mind was evidently wholly given to the Master and the Holy Mother. His serene countenance attracted monks and devotees, young and old alike, and all felt a sense of peace and joy in his presence.
Swami Santanandaji Maharaj attained mahasamadhi at the Ramakrishna Mission Seva Pratishthan, Calcutta, on the 17th of January 1974, at 8.21 a.m.