Flinter, an Irishman by birth, entered the British Army in 1811 as an ensign in the 7th West India regiment of foot, and was advanced to the rank of lieutenant on 22 July 1813. He was sent with his regiment to Curaçao in the West Indies in 1812, and in 1815 visited Caracas, then in the throes of an unusually bloody and exasperating civil war. Here he acted as interpreter to the British Embassy. In the following year he was placed on the half-pay list, and seeing no prospect of promotion in the British service, he fixed his residence at Caracas. He was treated with great distinction by the Spanish Captain-General Juan Manuel Cajigal, and he obtained employment as interpreter between the Spaniards, English and Americans. He afterwards travelled through most of the European colonies in the West Indies and on the continent of America, married a Spanish American lady through whom he acquired ownership of land and slaves and obtained a commission in the Spanish Army. Though he remained on the British half-pay list until 1832, he had for some years before that date held the position of a staff officer in the Spanish service, after which time he wrote a lengthy account about the colonies of Spain (Puerto Rico and Cuba) and his opinions about slave labour.