Marrant was born in New York City in 1755. Following the death of his father, he moved with his mother to Florida, Georgia and Charleston, South Carolina. He was able to read and spell by the age of 11. Marrant was taught how to play the French horn and violin, entertaining the local gentry at balls.

At the age of 13 Marrant was taken to hear Methodist preacher George Whitefield and was converted. After disagreements with his family about this, he wandered in the wilderness, relying on God to feed and protect him. He was found by a Cherokee hunter and taken to a Cherokee town, where he was sentenced to death. However, he was spared, allegedly due to the miraculous conversion of the executioner.

Marrant lived with the Cherokees for two years before returning to Charleston, where his own family didn't recognise him. He continued his missionary work with slaves, despite the objection of their owners, until the start of the American Revolution.

Marrant claimed that he was impressed into the Royal Navy for six years before being discharged in 1782, but official records do not show him as having served with the Navy. In 1782 Marrant started training as a Methodist minister with the Countess of Huntingdon's Connexion. He is shown on the New York City Inspection Roll of Negroes as the owner of Melia Marrant and two children, although Devona Mallory in African American Lives claims that these people were his family.

He was ordained in 1785 and sent to Nova Scotia to minister to several thousand African Americans who had fled north during the fighting.

Marrant moved to Boston, Massachusetts in 1787 before returning briefly in 1788 to Nova Scotia to marry Elizabeth Herries. In 1788 he became the chaplain of the Prince Hall Grand Lodge Free and Accepted Masons in Boston, a group which led the successful movement to abolish slavery in 1788.

Marrant traveled to London in 1790, and died in the suburb of Islington the following year.

In 1785 he published A Narrative of the Lord's Wonderful Dealings with John Marrant, A Black, with the assistance of Reverend William Aldridge, who transcribed it. This memoir proved to be very popular, going to 17 editions, although Marrant did not receive much financial benefit from it, as not all of the printings were authorised.

Critics have noted that the narrative has a very different tone to his later publications. However, Henry Louis Gates, Jr. has argued in The Signifying Monkey that many early African American narratives were transcribed by white editors, which would explain the different writing style.

Marrant delivered a sermon in 1789 noting the equality of men before God; it was published. His final published work was a 1790 journal.

• A Narrative of the Lord's Wonderful Dealings with John Marrant, A Black, 1785.

• A Sermon Preached on the 24th Day of June 1789...at the Request of the Right Worshipful the Grand Master Prince Hall, and the Rest of the Brethren of the African Lodge of the Honorable Society of Free and Accepted Masons in Boston, 1789.

• A Journal of the Rev. John Marrant, from August the 18th, 1785, to the 16th of March, 1790.