[2] Mendes was educated in Port of Spain until 1912, then at the age of 15 went to continue his studies in the United Kingdom, attending Hitchin Grammar School.

He served in the 1st Battalion, Rifle Brigade,[5] and fought for two years in Flanders, along the Belgian Front, and was awarded a Military Medal for distinguishing himself on the battlefield.

In fact, Sam Mendes explains that like the fictional soldiers' mission in 1917, Alfred Mendes also carried messages through the perilous territory of no-man's land, and the fact that he was only 5 feet 4 inches (163 cm) tall enabled him to avoid easy detection because the winter mist that shrouded the territory was often 6 feet (180 cm) high.

One remnant of his experience in mud-drenched trench warfare was his lifelong habit of continually washing his hands for several minutes at a time.

[8] Mendes returned to Trinidad in 1919, and worked in his wealthy father's provisions business, while spending his spare time writing poetry and fiction, and in establishing contact with other writers, artists and scholars.

Together with C. L. R. James, Mendes produced two issues of a pioneering literary magazine called Trinidad (Christmas 1929 and Easter 1930).

Mendes was quoted as saying in 1972: "James and I departed from the convention in the selection of our material, in the choice of a strange way of life, in the use of a new dialect.

While in the United States, he joined literary salons and associated with writers including Richard Wright, Countee Cullen, Claude McKay, William Saroyan, Benjamin Appel, Thomas Wolfe, Malcolm Lowry, Ford Madox Ford, William Faulkner, Sherwood Anderson, and James T.