The poet's health was frail, and after going through a Jesuit school in Lisbon and learning English, French and Italian at home, he proceeded in 1742 to the University of Coimbra with a view to a legal career.
In 1751 his marriage in Lisbon, Santa Justa, with Maria Ana Xavier Froes Mascarenhas de Sande Salema, born c. 1725, by whom he had one son, brought him a rich dowry which enabled him to live in ease and cultivate letters; but in later years a lawsuit reduced him to poverty.
In 1756, in conjunction with Cruz e Silva and others, Garção founded the Arcádia Lusitana to reform the prevailing bad taste in literature, identified with Seicentismo, which delighted in conceits, windy words and rhetorical phrases.
In the midst of his literary activity and growing fame, he was arrested on the night of April 9, 1771, and committed to prison by Pombal, whose displeasure he had incurred by his independence of character.
The immediate cause of his incarceration would appear to have been his connection with a love intrigue between a young friend of his and the daughter of a Colonel Elsden, but he was never brought to trial, and the matter must remain in doubt.
Taking Horace as his model, supported by his background of scholarship and wide reading, Garção set out to raise and purify the standard of poetic taste.
His two comedies in hendecasyllables, the Theatro Novo (played in January 1766) amid the Assemblea, are satires on the social life of the capital; and in the Cantata de Dido, included in the latter piece, the spirit of Greek art is allied to the perfection of form, making this composition much-admired among Portuguese 18th century poetry.