Barber was born a slave in Jamaica on a sugarcane plantation belonging to the Bathurst family. His original name was Quashey, which was a common name for a male slave.
At the age of about 15, he was brought to England by his owner, Colonel Richard Bathhurst, whose son, also called Richard, was a close friend of Johnson. Barber was sent to school in Yorkshire. Johnson's wife Elizabeth died in 1752, plunging Johnson into a depression that Barber later vividly described to James Boswell. The Bathursts sent Barber to Johnson as a valet, arriving two weeks after her death. Although the legal validity of slavery in England was ambiguous at this time (with Somersett's Case of 1772 clarifying that it did not exist in England), when the elder Bathurst died two years later he gave Barber his freedom in his will, with a small legacy of £12 (equivalent to £2,000 in 2015). Johnson himself was an outspoken opponent of slavery, not just in England but in the American colonies as well.
Barber then went to work for an apothecary in Cheapside but kept in touch with Johnson. He later signed up as a sailor for the Navy. He served as a "landman" aboard various ships, received regular pay and good reports, saw the coast of Britain from Leith to Torbay, and acquired a taste for tobacco. He was discharged "three days before George II died", in other words on 22 October 1760, and with a pipe between his teeth and a roll in his gait, he returned to London and to Johnson to be his servant. Barber's brief maritime career is known from James Boswell's Life of Johnson:
Later Johnson put Barber, by then in his early thirties, in a school, presumably so that he could act as Johnson's assistant. From Boswell's Life:
Barber is often mentioned in James Boswell's Life of Johnson and other contemporary sources, and there are at least two versions of a portrait, one now in Dr. Johnson's House, which may be of him. Most recent art historians thought it was probably painted by James Northcote, or perhaps by Northcote's master Sir Joshua Reynolds, who was one of Barber's Trustees under the will. An alternative view, recently expressed on a BBC programme, is that it is by Reynolds himself, but of his own black servant, not Barber.
When making his will, Johnson asked Sir John Hawkins, later his first biographer, what provision he should make for Barber. Sir John said that a nobleman would give 50 pounds a year (equivalent to £6,000 in 2015). Then I shall be "noblissimus" replied Johnson, and give him 70 (equivalent to £8,000 in 2015). Hawkins disapproved, and after Johnson's death criticised his "ostentatious bounty [and] favour to negroes". The bequest was indeed widely covered in the press. Johnson, in fact, left £750 (equivalent to £83,000 in 2015) in the trust of his friend Bennet Langton from which he was expected to pay an annuity.
Barber moved with his family to a rented terrace house in Lichfield, Johnson’s birthplace, where – as a Gentleman's Magazine correspondent reported – he spent his time "in fishing, cultivating a few potatoes, and a little reading". Later he opened up a small village school in nearby Burntwood. The money from his inheritance did not last and Barber sold off his store of Johnson memorabilia to defray his debts. He died in Stafford on 13 January 1801 due to an unsuccessful operation at Staffordshire Royal Infirmary. He was survived by his son, Samuel Barber, his daughter, Ann, and his wife, Elizabeth. His descendants still farm near Lichfield.
Francis Barber's marriage to Elizabeth Ball is featured in the short silent animation The Trouble with Francis (2000), whilst Barber also appears as a character in the 2015 play Mr Foote's Other Leg.