John Gay was born on September 16th, 1685, the youngest of five children of William and a daughter of Jonathan Hanmer, of whom all but the first lived to adulthood. He was born into relative privilege, but orphaned at the age of ten with the death of his father (his mother having passed a year earlier). He then was seperated from his siblings and sent to live with his paternal uncle, Thomas Gay of Barnstaple.
It is unknown how long Gay remained with his uncle in Barnstaple; however, it is generally accepted that, upon leaving, he was apprenticed to a silk-mercer in London. This employment didn't last long, however, and Gay returned to Barnstaple, this time to his maternal uncle, Reverend John Hanmer, pastor of the Church of England in Barnstaple.
Gay returned to London sometime around 1706. He remained a private gentleman until 1712, when he took the position of steward to the Duchess of Monmouth. He remained with her until 1714, when, with the help of Johnathan Swift, he secured the position of secretary to Lord Clarendon. He is known to have visited the continent during this time; he attempted to advance himself in diplomatic service to the Hanoverian court, but was prevented from this by the death of the Queen. From then on, until near the end of his life, he remained financially independent, a matter of some concern and difficulty to him. His financial difficulties were compounded by the loss of his fortunes, such as they were, in the South Sea Bubble. He did not become financially stable again until 1728; he did, however, manage the £800 profit from The Beggar's Opera well enough to provide for himself until the end of his life in 1732.
Gay's relationship with the Scriblerians, a social/philosophical club focused on returning to classical, elitist ideals of literary accomplishment, began early in his career. It is known for certain that he met Alexander Pope in 1711, and Swift somewhat earlier, and kept up correspondence with them to the end of his life.
A more complete biography and analysis of John Gay's life and correspondance may be found in "Life and Letters of John Gay which is available online at Project Gutenburg (Mirrored here)
It is unquestionable that John Gay's financial situation influenced his work heavily. Almost all his works, large or small, have some aspect of their form shaped by his desire for patronage, and his failure to attain it. Johnson's Lives of the English Poets states that:
Gay in that disastrous year had a present from young Craggs of some South-sea-stock, and once supposed himself to be master of twenty thousand pounds. His friends persuaded him to sell his share, but he dreamed of dignity and splendour, and could not bear to obstruct his own fortune. He was then importuned to sell as much as would purchase an hundred a year for life, 'which,' says Fenton, 'will make you sure of a clean shirt and a shoulder of mutton every day.' This counsel was rejected, the profit and principal were lost, and Gay sunk under the calamity so low that his life became in danger.
By the care of his friends, among whom Pope appears to have shewn particular tenderness, his health was restored; and, returning to his studies, he wrote a tragedy called The Captives, which he was invited to read before the princess of Wales. When the hour came he saw the princess and her ladies all in expectation, and advancing with reverence, too great for any other attention, stumbled at a stool, and falling forwards threw down a weighty Japan screen. The princess started, the ladies screamed, and poor Gay after all the disturbance was still to read his play.
The fate of The Captives, which was acted at Drury-Lane in 1723, I know not; but he now thought himself in favour, and undertook (1726) to write a volume of Fables for the improvement of the young duke of Cumberland. For this he is said to have been promised a reward, which he had doubtless magnified with all the wild expectations of indigence and vanity.
Next year the Prince and Princess became King and Queen, and Gay was to be great and happy; but upon the settlement of the household he found himself appointed gentleman usher to the princess Louisa. By this offer he thought himself insulted, and sent a message to the Queen, that he was too old for the place. There seem to have been many machinations employed afterwards in his favour; and diligent court was paid to Mrs. Howard, afterwards countess of Suffolk, who was much beloved by the King and Queen, to engage her interest for his promotion; but solicitations, verses, and flatteries were thrown away; the lady heard them, and did nothing.
Gay is often connected very directly with the hare in "Fable L; The Hare and Many Friends" and with good reasons, the most obvious being the explicit "A hare, who, in a civil way, Complied with ev'ry thing, like Gay." This sense of abandonment by those who are expected to support on, one's friends (or patrons), informs The Beggar's Opera as well. In Act III, scene 14, while Macheath is imprisoned in Newgate and awaiting his sentence, Matt of the Mint and Ben Budge, members of Macheath's gang, come to visit him in his cell. He askes them a final favor; but, to the audience's knowledge, nothing comes of it. Throughout the play, personal relationships, although presented more positively than professional, produce no effective help or relief.