On June 30, 1766 António Leal entered on the Seminary of the Patriarchate of Lisbon, where he was a student of John de Sousa Carvalho. In 1775 he became an assistant of his teacher and organist. In 1787 is chapel master and on May 19, 1777 directed his first sacred work, the Mass of the Holy Spirit, which was sung during the acclaim of Queen Maria I of Portugal.
On 8 August the same year he was admitted as a member of the union of musicians from Lisbon, the Brotherhood of St Cecilia. Most of his sacred music was composed for the Royal Chapel and from 1782 he began to write serenades, who were represented in the palaces of Queluz and Ajuda.
In 1790 he became musical director of the Theatre of Rua dos Condes, where they were representing performances of Italian operas. Three years later the palace financier Anselmo José da Cruz Sobral in Lisbon debut drama Il natale august, among several singers who participated remember the Portuguese mezzo-soprano Luisa Todi.
Moreira, in 1793 became the first of the new music director of Teatro São Carlos, where he represented his work with text in Portuguese, A vingança da Cigana (1794). In 1799 left the direction of São Carlos to Marcos Portugal and Francesco Federici. The following year, contributed to the production "pasticcio" Il disertore francese,, which went on stage at the Teatro Carignano in Turin and Scene La Scala in Milan.