In 1940, Brahmachari Rabinarayan mastered kechari, bhramari, and shambhavi. During this time, an effulgence of supernatural divine light started glowing around his body, producing ineffable awe and spiritual ecstasy in many. In 1940 and 1941, he learned the third level of Kriya Yoga from Swami Satyananda Giri. From 1943 to 1945, the last higher Kriya initiations were given by Shrimat Bhupendranath Sanyal, a realized householder disciple of Lahiri Mahasaya. In 1944, he was taught some intricacies of meditation and spiritual life by a mysterious, anonymous yogi. From 1946 to 1948, he attained different states of samadhi, including nirvikalpa samadhi.
After following a strict spiritual practice of sincere meditation and maintaining silence for many years, Mahavatar Babaji Maharaj graced him with two long-cherished visits in 1949 at Karar Ashram, showering him with blessings and prophesizing that his mission would be to spread Kriya Yoga to the East and West. He later traveled to the famous Ranikhet in the Himalayas to visit Babaji Maharaj, but only heard Babaji's voice instruct him to spread Kriya Yoga throughout the world.
In 1950, he was appointed by Paramahamsa Yogananda as the acharya of the Karar Ashram. From that day on, he worked tirelessly for the spiritual advancement of the disciples on the spiritual path. Aware of his spiritual attainment, in 1951 Paramahamsa Yogananda empowered Brahmachari Rabinarayan to initiate sincere seekers into Kriya Yoga. Thus, he started his long missionary work that took him to the length and breadth of his beloved India. He was also blessed with the highest spiritual attainment, the paramahamsa stage.
On September 27, 1958, Mother Goddess Kali, his presiding deity, appeared before him with all effulgence of light and radiant splendor, instructing him to work ceaselessly for the spiritual uplifting of the world, assuring him of her blessings on his work teaching Kriya Yoga.
On his fifty-second birthday on May 27, 1959, he was initiated into sannyasa by the world renowned sannyasi Jagadguru Bharati Krishna, the Shankaracharya of Gobardhana Peetha, Puri. Casting off his previous name Brahmachari Rabinarayan, he became Swami Hariharananda Giri.
He was later crowned sadhu sabhapati (president) of the Karar Ashram amidst the loud applause and approval of many sadhakas,sadhus, and the Shankaracharya. His spiritual life illustrates the synthesis of karma, jnana, and bhakti practices.