Brull was born in Camagüey, in eastern Cuba, where his father, Miguel Brull, a Spanish army officer, was stationed. His mother, Celia Caballero, was descended from a family that had resided in Cuba for many generations.
As a child he lived in Ceuta and Málaga in Spain. It was during his teenage years, as a student in Camagüey, that he discovered his passion for poetry. He and other students founded a short-lived magazine for which they wrote poems and essays. Eagerly reading all the poetry he could, young Brull was especially struck by the work of the French Symbolist poets.
In 1908 he moved to Havana where he attended the university, graduating with a Doctor of Law degree at age 22. He worked in a law office but also wrote poetry for the magazine El Fígaro. During 1914 and 1915 he was a member of the small group that formed around the Dominican literary critic, Pedro Henríquez Ureña. Henríquez, believing Brull had a future as a poet, became his mentor, introducing him to editors and suggesting he read poets whom Brull was not familiar with.
In 1916 Brull published his first book of poetry, La casa del silencio. Shortly afterwards he married Adela Baralt and, switching careers, entered the Cuban diplomatic service. Brull was determined to leave Cuba where, exhausted by years fighting for independence and preoccupied by problems facing any new country, the arts were confused and anemic, uninterested in the great experiments (Cubism, futurism, etc.) taking place in Europe.
Though impatient to reach Europe, the first two countries he was sent to as a diplomat were the United States and Peru. In the mid 20s he was stationed in Madrid. There he had the good fortune to participate in the reunions of the literary cafés frequented by many of the best poets Spain was to produce in the 20th century: Federico García Lorca, Rafael Alberti, Jorge Guillén, Vicente Aleixandre, and many others. While in Madrid, some of Brull's early poetry was published in Paris in a French translation.
In 1923 Brull joined about 60 young professionals of Havana who decided to take a public stance against the reigning passivity and mediocrity in politics and culture. Called El Grupo Minorista (the Minority Group), they demanded an end to years of cultural backwardness and an aggressive affirmation of the new artistic tendencies coming out of Europe. In politics, they denounced dictatorships and called for the formation of a Cuban government more responsive to the people.
In 1928 he published his second book of poetry, Poemas en menguante. Though also published in Paris, where he was now living, it was written in Spanish. All of his books were small editions for friends and family, paid for out of his pocket.
The Brulls lived in Paris from 1927 to 1934 with only two interruptions: a year, each, in Berne and Havana. The return of the Brulls to Havana coincided with numerous riots and demonstrations as students clashed with the police of the government of President Gerardo Machado, an increasingly ruthless dictator.
Brull spent the Great Depression back in Paris. Two or three times a year found him traveling. He frequently visited Havana, on business; southern Spain, the land of his childhood; and Mexico City where he called on his friends Gabriela Mistral, the Chilean poet, Alfonso Reyes, the Mexican man-of-letters, and others.
In 1934 his third book of poetry, Canto redondo, was brought out in Paris. He was stationed in Rome between 1934 and 1937 where fascism was alive and thriving.
After moving to Brussels (for the second time) at the end of the 1930s, Brull was in charge of attending to the many German Jews who, seeking visas to emigrate, had lined up before the legations and embassies of numerous countries. During these years he was Cuba's delegate to the XVII Reunion of the Assembly of the League of Nations and, also, Commissioner for the repatriation of Cubans fleeing the Spanish Civil War. Brull had decided that an all-European war was imminent—though most of his colleagues and friends disagreed—and pressured the Ministry to be sent back to Havana. He left in June, 1939. The ship carrying all of the Brull's household effects to Cuba, a year later, was torpedoed by the Germans and sank.
In 1939, a bilingual (French-Spanish) book, Poëmes, came out in Paris, with a preface written by one of the greatest literary figures of France at the time, Paul Valéry. Brull worked for many years on a translation into Spanish of Valéry's most famous, and difficult, poems: "Le Cimetiére Marin" (The Graveyard by the Sea) and "La Jeune Parque" (The Young Fate).
In Cuba, Brull was one of the principal organizers of a conference of the International Institute of Intellectual Cooperation, held in 1941. This organization was made up of major intellectuals who believed that the interchange of ideas would help lead to a solution to the tension of the 1930s and the violence of the Second World War. Brull admired people who were capable of both action and thought. He had no use for the static attitude of Rodin´s famous statue, "The Thinker". Brull's hero was the Cuban journalist and poet, José Martí, who was responsible for organizing the Cuban resistance to Spain and died in a skirmish with Spanish soldiers during the War of Independence.
His fifth book of poetry, Solo de rosa, appeared. His poems also were printed in the foremost literary publications: Social, Gaceta del Caribe, Espuela de Plata, Clavileño, Orígenes and El Fígaro. He had long conversations with the exiled Spanish poet, Juan Ramón Jiménez, who wrote a similar type of poetry.
During the Second World War, Brull was stationed in Washington, D.C., and in 1945 was sent to Ottawa to establish the first Cuban diplomatic mission in Canada.
In Brussels, once more, in 1950, he published Temps en peine. Tiempo en pena, a bilingual edition. Here, too, his wife died after many years of fighting cancer.
His last post was as Cuban ambassador to Uruguay. However, he refused to comply with an order from the Cuban dictator, Fulgencio Batista, and he resigned abruptly, ending a career of 47 years in the Cuban diplomatic service. That same year (1954) the final book of poems he would publish, Rien que... (Nada más que...), came out in Paris.
Back in Havana, he turned to modernizing the cattle ranch he had inherited from his mother. But a growing brain tumor weakened him bit by bit and eventually left him in a coma. He died at the age of 65 in 1956.