Ramakrishna was born on 18 February 1836, in the village of Kamarpukur, in the Hooghly district of West Bengal, into a very poor, pious, and orthodox Brahmin family. Kamarpukur was untouched by the glamour of the city and contained rice fields, tall palms, royal banyans, a few lakes, and two cremation grounds. His parents were Khudiram Chattopadhyay and Chandramani Devi. According to his followers, Ramakrishna's parents experienced supernatural incidents and visions before his birth. In Gaya his father Khudiram had a dream in which Lord Gadadhara (a form of Vishnu), said that he would be born as his son. Chandramani Devi is said to have had a vision of light entering her womb from Shiva's temple.

Ramakrishna's father died in 1843, after which family responsibilities fell on his elder brother Ramkumar. This loss drew him closer to his mother, and he spent his time in household activities and daily worship of the household deities and became more involved in contemplative activities such as reading the sacred epics. When Ramakrishna was in his teens, the family's financial position worsened. Ramkumar started a Sanskrit school in Kolkata and also served as a priest. Ramakrishna moved to Kolkata in 1852 with Ramkumar to assist in the priestly work.

In 1855 Ramkumar was appointed as the priest of Dakshineswar Kali Temple, built by Rani Rashmoni—a rich woman of Kolkata who belonged to the kaivarta community. Ramakrishna, along with his nephew Hriday, became assistants to Ramkumar, with Ramakrishna given the task of decorating the deity. When Ramkumar died in 1856, Ramakrishna took his place as the priest of the Kali temple.

In 1861, Ramakrishna accepted Bhairavi Brahmani, an orange-robed, middle-aged female ascetic, as a Teacher. She carried with her the Raghuvir Shila, a stone icon representing Ram and all Vaishnava deities. She was thoroughly conversant with the texts of Gaudiya Vaishnavism and practised Tantra. According to the Bhairavi, Ramakrishna was experiencing phenomena that accompany mahabhava, the supreme attitude of loving devotion towards the Divine, and quoting from the bhakti shastras, she said that other religious figures like Radha and Chaitanya had similar experiences.

Max Müller, Mahatma Gandhi, Jawaharlal Nehru, Sri Aurobindo, and Leo Tolstoy have acknowledged Ramakrishna's contribution to humanity. Ramakrishna's influence is also seen in the works of artists such as Franz Dvorak(1862–1927) and Philip Glass.

The Bhairavi initiated Ramakrishna into Tantra. Tantrism focuses on the worship of shakti and the object of Tantric training is to transcend the barriers between the holy and unholy as a means of achieving liberation and to see all aspects of the natural world as manifestations of the Divine shakti. Under her guidance, Ramakrishna went through sixty four major tantric sadhanas which were completed in 1863. He began with mantra rituals such as japa and purascarana and many other rituals designed to purify the mind and establish self-control. He later proceeded towards tantric sadhanas, which generally include a set of heterodox practices called vamachara (left-hand path), which utilise as a means of liberation, activities like eating of parched grain, fish and meat along with drinking of wine and sexual intercourse. According to Ramakrishna and his biographers, Ramakrishna did not directly participate in the last two of those activities (some even say he didn't indulge in meat eating), all that he needed was a suggestion of them to produce the desired result. Ramakrishna acknowledged the left-hand tantric path, though it had "undesirable features", as one of the "valid roads to God-realization", he consistently cautioned his devotees and disciples against associating with it. The Bhairavi also taught Ramakrishna the kumari-puja, a form of ritual in which the Virgin Goddess is worshiped symbolically in the form of a young girl. Under the tutelage of the Bhairavi, Ramakrishna also learnt Kundalini Yoga. The Bhairavi, with the yogic techniques and the tantra played an important part in the initial spiritual development of Ramakrishna.

In 1864, Ramakrishna practised vātsalya bhāva under a Vaishnava guru Jatadhari. During this period, he worshipped a metal image of Ramlālā (Rama as a child) in the attitude of a mother. According to Ramakrishna, he could feel the presence of child Rama as a living God in the metal image.

In 1865, Ramakrishna was initiated into sannyasa by Totapuri, an itinerant monk who trained Ramakrishna in Advaita Vedanta, the Hindu philosophy which emphasises non-dualism.

According to Swami Saradananda's biography, in 1866 Govinda Roy, a Hindu guru who practised Sufism, initiated Ramakrishna into Islam, and he practiced Islam for three days. During this practice, Ramakrishna had a vision of a luminous figure, and Swami Nikhilananda's biography speculates that the figure was 'perhaps Mohammed'. According to these accounts, Ramakrishna "devoutly repeated the name of Allah, wore a cloth like the Arab Muslims, said their prayer five times daily, and felt disinclined even to see images of the Hindu gods and goddesses, much less worship them—for the Hindu way of thinking had disappeared altogether from my mind." After three days of practice he had a vision of a "radiant personage with grave countenance and white beard resembling the Prophet and merging with his body". Kripal writes that this "would have been a heretical experience through and through" for most Muslims.

At the end of 1873 he started the practice of Christianity, when his devotee Shambu Charan Mallik read the Bible to him. According to Swami Saradananda's biography, Ramakrishna was filled with Christian thoughts for three days and no longer thought of going to the Kali temple. Ramakrishna described a vision in which a picture of the Madonna and Child became alive and he had a vision in which Jesus merged with his body. In his own room amongst other Divine pictures was one of Christ, and he burnt incense before it morning and evening. There was also a picture showing Jesus Christ saving St Peter from drowning in the water.

In 1875, Ramakrishna met the influential Brahmo Samaj leader Keshab Chandra Sen. Keshab had accepted Christianity, and had separated from the Adi Brahmo Samaj. Formerly, Keshab had rejected idolatry, but under the influence of Ramakrishna he accepted Hindu polytheism and established the "New Dispensation" (Nava Vidhan) religious movement, based on Ramakrishna's principles—"Worship of God as Mother", "All religions as true" and "Assimilation of Hindu polytheism into Brahmoism". Keshab also publicised Ramakrishna's teachings in the journals of New Dispensation over a period of several years, which was instrumental in bringing Ramakrishna to the attention of a wider audience, especially the Bhadralok (English-educated classes of Bengal) and the Europeans residing in India.

As his name spread, an ever-shifting crowd of all classes and castes visited Ramakrishna. Most of Ramakrishna's prominent disciples came between 1879–1885. Apart from the early members who joined the Ramakrishna Order, his chief disciples consisted of:

In the beginning of 1885 Ramakrishna suffered from clergyman's throat, which gradually developed into throat cancer. He was moved to Shyampukur near Kolkata, where some of the best Physicians of the time, including Dr. Mahendralal Sarkar, were engaged. When his condition aggravated he was relocated to a large garden house at Cossipore on 11 December 1885.

During his last days, he was looked after by his monastic disciples and Sarada Devi. Ramakrishna was advised by the doctors to keep the strictest silence, but ignoring their advice, he incessantly conversed with visitors. According to traditional accounts, before his death, Ramakrishna transferred his spiritual powers to Vivekananda and reassured Vivekananda of his avataric status. Ramakrishna asked Vivekananda to look after the welfare of the disciples, saying, "keep my boys together" and asked him to "teach them". Ramakrishna also asked other monastic disciples to look upon Vivekananda as their leader. Ramakrishna's condition gradually worsened, and he died in the early morning hours of 16 August 1886 at the Cossipore garden house. According to his disciples, this was mahasamadhi. After the death of their master, the monastic disciples led by Vivekananda formed a fellowship at a half-ruined house at Baranagar near the river Ganges, with the financial assistance of the householder disciples. This became the first Math or monastery of the disciples who constituted the first Ramakrishna Order.

The principal source for Ramakrishna's teaching is Mahendranath Gupta's Sri Sri Ramakrishna Kathamrita, which is regarded as a Bengali classic. Kripal calls it "the central text of the tradition" The text was published in five volumes from 1902 to 1932. Based on Gupta's diary notes, each of the five volumes purports to document Ramakrishna's life from 1882–1886.

Other organisations include the Ramakrishna Vedanta Society founded by Swami Abhedananda in 1923, the Ramakrishna Sarada Math founded by a rebel group in 1929, the Ramakrishna Vivekananda Mission formed by Swami Nityananda in 1976, and the Sri Sarada Math and Ramakrishna Sarada Mission founded in 1959 as a sister organisation by the Ramakrishna Math and Mission.

The dialogue on psychoanalysis and Ramakrishna began in 1927 when Sigmund Freud's friend Romain Rolland wrote to him that he should consider spiritual experiences, or "the oceanic feeling," in his psychological works. Romain Rolland described the mystical states achieved by Ramakrishna and other Mystics as an "'oceanic' sentiment", one which Rolland had also experienced. Rolland believed that the universal human religious emotion resembled this "oceanic sense." In his 1929 book La vie de Ramakrishna, Rolland distinguished between the feelings of unity and eternity which Ramakrishna experienced in his mystical states and Ramakrishna's interpretation of those feelings as the goddess Kali.

During the 1937 Parliament of Religions, which was held at the Ramakrishna Mission in Calcutta, Tagore acknowledged Ramakrishna as a great saint because

In his 1991 book The Analyst and the Mystic, Indian psychoanalyst Sudhir Kakar saw in Ramakrishna's visions a spontaneous capacity for creative experiencing. Kakar also argued that culturally relative concepts of eroticism and gender have contributed to the Western difficulty in comprehending Ramakrishna. Kakar saw Ramakrishna's seemingly bizarre acts as part of a bhakti path to God.

These views were disputed by Swami Atmajnanananda, who wrote that Jivanavrttanta had been reprinted nine times in Bengali as of 1995, and other scholars and psychoanalysts, including Romain Rolland, Alan Roland, Kelly Aan Raab, Somnath Bhattacharyya, J.S. Hawley

Ramakrishna is considered an important figure in the Bengali Renaissance of 19th–20th century. Several organisations have been established in his name. The Ramakrishna Math and Mission is the main organisation founded by Swami Vivekananda in 1897. The Mission conducts extensive work in health care, disaster relief, rural management, tribal welfare, elementary and higher education. The movement is considered as one of the revitalisation movements of India. Amiya Sen writes that Vivekananda's "social Service gospel" stemmed from direct inspiration from Ramakrishna and rests substantially on the "liminal quality" of the Master's message.

In the Kolkata scene of the mid to late nineteenth century, Ramakrishna was opinionated on the subject of Chakri. Chakri can be described as a type of low-paying servitude done by educated men—typically government or commerce-related clerical positions. On a basic level, Ramakrishna saw this system as a corrupt form of European social organisation that forced educated men to be servants not only to their bosses at the office but also to their wives at home. What Ramakrishna saw as the primary detriment of Chakri, however, was that it forced workers into a rigid, impersonal clock-based time structure. He saw the imposition of strict adherence to each second on the watch as a roadblock to spirituality. Despite this, however, Ramakrishna demonstrated that Bhakti could be practised as an inner retreat to experience solace in the face of Western-style discipline and often discrimination in the workplace.

Vivekananda portrayed Ramakrishna as an Advaita Vedantin. Vivekananda's approach can be located in the historical background of Ramakrishna and Calcutta during the mid-19th century. Neevel notes that the image of Ramakrishna underwent several transformations in the writings of his prominent admirers, who changed the 'religious madman' into a calm and well-behaving proponent of Advaita Vedanta. Narasingha Sil has argued that Vivekananda revised and mythologised Ramakrishna's image after Ramakrishna's death. McDaniel notes that the Ramakrishna Mission is biased towards Advaita Vedanta, and downplays the importance of Shaktism in Ramakrishna's spirirtuality. Malcolm McLean argued that the Ramakrishna Movement presents "a particular kind of explanation of Ramakrishna, that he was some kind of neo-Vedantist who taught that all religions are the same."