He began conspiring with the French, and helped force the Portuguese court to flee to Brazil in 1807.

On 15 February 1808 he was named inspector general of all Portuguese forces, and commanded them in Spain from March to June 1808.

He entered France in July 1811 and was assigned to the Observation Corps of the Grande Armée on 30 January 1812.

Named major general in the service of France on 21 March 1812, Almeida was put in charge of the 2nd company of Portuguese chasseur.

Almeida married Henriqueta Julia Gabriela da Cunha (1787-1829), eldest daughter of the Count of São Vicente, on 19 February 1782 in Lisbon.