According to Carretta, Vassa's baptismal record and a naval muster roll document him as from South Carolina. Carretta interpreted these anomalies as possible evidence that Equiano had made up the account of his African origins, and adopted material from others. But, Paul Lovejoy, Alexander X. Byrd, and Douglas Chambers note how many general and specific details Carretta can document from sources that related to the slave trade in the 1750s as described by Equiano, including the voyages from Africa to Virginia, sale to Captain Michael Henry Pascal in 1754, and others. They conclude he was more likely telling what he understood as fact than creating a fictional account; his work is shaped as an autobiography.

In Virginia, Equiano was bought in 1754 by Michael Pascal, a lieutenant in the Royal Navy. Pascal renamed the boy "Gustavus Vassa", after the Swedish noble who had become Gustav I of Sweden, king in the sixteenth century. Equiano had already been renamed twice: he was called Michael while on board the slave ship that brought him to the Americas; and Jacob, by his first owner. This time, Equiano refused and told his new owner that he would prefer to be called Jacob. His refusal, he says, "gained me many a cuff" – and eventually he submitted to the new name. He used this name for the rest of his life, including on all official records. He only used Equiano in his autobiography.

At this time, Equiano converted to Christianity. He was baptised at St Margaret's, Westminster, on 9 February 1759, when he was described in the parish register as "a Black, born in Carolina, 12 years old". His godparents were Mary Guerin and her brother, Maynard, who were cousins of his master Pascal. They had taken an interest in him and helped him to learn English. Later, when Equiano's origins were questioned after his book was published, the Guerins testified to his lack of English when he first came to London.

Robert King set Equiano to work on his shipping routes and in his stores. In 1765, when Equiano was about 20 years old, King promised that for his purchase price of 40 pounds (equivalent to £5,000 in 2016) he could buy his freedom. King taught him to read and write more fluently, guided him along the path of religion, and allowed Equiano to engage in profitable trading for his own account, as well as on his owner's behalf. Equiano sold fruits, glass tumblers, and other items between Georgia and the Caribbean islands. King allowed Equiano to buy his freedom, which he achieved in 1767. The merchant urged Equiano to stay on as a Business partner. However, Equiano found it dangerous and limiting to remain in the British colonies as a freedman. While loading a ship in Georgia, he was almost kidnapped back into enslavement.

By about 1768, Equiano had gained his freedom and went to England. He continued to work at sea, travelling sometimes as a deckhand based in England. In 1773 on the British Royal Navy ship Racehorse, he travelled to the Arctic in an expedition to find a northern route to India. On that voyage he worked with Dr. Charles Irving, who had developed a process to distill seawater and later made a fortune from it. Two years later, Irving recruited Equiano for a project on the Mosquito Coast in Central America, where he was to use his African background to help select slaves and manage them as labourers on sugar cane plantations. Irving and Equiano had a working relationship and friendship for more than a decade, but the plantation venture failed.

Several events in Equiano's life led him to question his faith. He was severely distressed in 1774 by the kidnapping of his friend, a black cook named John Annis, who was taken forcibly off the English ship Anglicania on which they were both serving. His friend's kidnapper, a Mr. Kirkpatrick, did not abide by the decision in the Somersett Case (1772), that slaves could not be taken from England without their permission, as Common law did not support the institution. Kirkpatrick had Annis transported to Saint Kitts, where he was punished severely and worked as a plantation labourer until he died. With the aid of Granville Sharp, Equiano tried to get Annis released before he was shipped from England, but was unsuccessful. He heard that Annis was not free from suffering until he died in slavery. Despite his questioning, he affirms his faith in Christianity, as seen in the penultimate sentence of his work that quotes the prophet Micah: "After all, what makes any event important, unless by its observation we become better and wiser, and learn 'to do justly, to love mercy, and to walk humbly before God?'"

In his account, Equiano also told of his settling in London. He married an English woman and lived with her in Soham, Cambridgeshire, where they had two daughters. He became a leading abolitionist in the 1780s, lecturing in numerous cities against the slave trade. Equiano records his and Granville Sharp's central roles in the anti-slave trade movement, and their effort to publicize the Zong massacre, which became known in 1783.

In the years following United States' gaining independence, in 1783 Equiano became involved in helping the Black Poor of London, who were mostly those African-American slaves freed during and after the American Revolution by the British. There were also some freed slaves from the Caribbean, and some who had been brought by their owners to England, and freed later after the decision that Britain had no basis in Common law for slavery. The black community numbered about 20,000. After the Revolution some 3,000 former slaves had been transported from New York to Nova Scotia, where they became known as Black Loyalists, among other Loyalists also resettled there. Many of the freedmen found it difficult to make new lives in London and Canada.

Equiano expanded his activities in London, learning the French horn and joining debating societies, including the London Corresponding Society. He continued his travels, visiting Philadelphia in 1785 and New York in 1786.

Entitled The Interesting Narrative of the Life of Olaudah Equiano, or Gustavus Vassa, the African (1789), the book rapidly went through nine editions in his lifetime. It is one of the earliest-known examples of published writing by an African Writer to be widely read in England. By 1792, it was a best seller: it has been published in Russia, Germany, Holland, and the United States. It was the first influential slave narrative of what became a large literary genre. But Equiano's experience in slavery was quite different from that of most slaves; he did not participate in field work, he served his owners personally and went to sea, was taught to read and write, and worked in trading.

After settling in England, Equiano decided to marry and have a family. On 7 April 1792, he married Susannah Cullen, a local woman, in St Andrew's Church in Soham, Cambridgeshire. The original marriage register containing the entry for Vassa and Cullen is held today by the Cambridgeshire Archives and Local Studies at the County Record Office in Cambridge. He included his marriage in every edition of his autobiography from 1792 onwards. Critics have suggested he believed that his marriage symbolised an expected commercial union between Africa and Great Britain. The couple settled in the area and had two daughters, Anna Maria (1793–1797) and Joanna (1795–1857).

Equiano's will provided for projects he considered important. In case of his surviving daughter's death before reaching the age of majority (21), he bequeathed half his wealth to the Sierra Leone Company for continued assistance to West Africans, and half to the London Missionary Society, which promoted education overseas. This organization had formed in November 1796 at the Spa Fields Chapel of the Countess of Huntingdon in north London. By the early 19th century, The Missionary Society had become well known worldwide as non-denominational; many of its members were Congregational.

Equiano died on 31 March 1797 and was buried at Whitefield's Methodist chapel on 6 April. One of his last addresses appears to have been at the Plaisterers' Hall in the City of London, where he drew up his will on 28 May 1796. He moved to John Street, Tottenham Court Road, close to Whitefield's Methodist chapel. (It was renovated in the 1950s for use by Congregationalists, now the site of the American International Church.) Lastly, he lived in Paddington Street, Middlesex, where he died. Equiano's death was reported in newspaper obituaries.

Following publication in 1967 of a newly edited version of his memoir by Paul Edwards, interest in Equiano was revived; additional editions of his work have been published since then. Nigerian scholars have also begun studying him. He was especially valued as a pioneer in asserting "the dignity of African life in the white society of his time."

In researching his life, some scholars since the late 20th century have disputed Equiano's account of his origins. In 1999, Vincent Carretta, a professor of English editing a new version of Equiano's memoir, found two records that led him to question the former slave's account of being born in Africa. He first published his findings in the journal Slavery and Abolition. At a 2003 conference in England, Carretta defended himself against Nigerian academics, like Obiwu, who accused him of "pseudo-detective work" and indulging "in vast publicity gamesmanship". In his 2005 biography, Carretta suggested that Equiano may have been born in South Carolina rather than Africa, as he was twice recorded from there. Carretta wrote:

Numerous works about Equiano have been produced for and since the 2007 bicentenary of Britain's abolition of the slave trade:

According to his memoir, Equiano recounted an incident when an attempted kidnapping of children was foiled by adults in his Igbo village, Isseke (Anambra State), in the southeastern part of present-day Nigeria. When he was around the age of eleven, he and his sister were left alone to look after their family premises – as was Common when adults went out of the house to work. They were both kidnapped and taken far away from their hometown of Essaka, separated and sold to slave traders. After changing ownership several times, Equiano met his sister again, but they were separated once more, and he was taken across a large river to the coast, where he was held by European slave traders. He was transported with 244 other enslaved Africans across the Atlantic Ocean to Barbados in the West Indies. He and a few other slaves were sent further away to the British colony of Virginia. Literary scholar Vincent Carretta argued in his 2005 biography of Equiano that the Activist could have been born in colonial South Carolina rather than Africa based on his discovery of a 1759 parish baptismal record that lists Equiano's place of birth as Carolina and a 1773 ship's muster that indicates South Carolina. A number of scholars agree with Carretta, while his conclusion is disputed by other scholars who believe the weight of evidence supports Equiano's account of coming from Africa.

Other historians also argue that the fact that many parts of Equiano's account can be proven lends weight to accepting his account of African birth. As Historian Adam Hochschild has written: "In the long and fascinating history of autobiographies that distort or exaggerate the truth. ...Seldom is one crucial portion of a memoir totally fabricated and the remainder scrupulously accurate; among autobiographers... both dissemblers and truth-tellers tend to be consistent." He also noted that "since the ‘rediscovery’ of Vassa’s account in the 1960s, ‘scholars have valued it as the most extensive account of an eighteenth-century slave’s life’ and the difficult passage from slavery to freedom."