Jiménez was born in Moguer, near Huelva, in Andalucia, on 24 December 1881. He studied law at the University of Seville, but he declined to put this training to use. He published his first two books at the age of eighteen, in 1900. The death of his father the same year devastated him, and a resulting depression led to his being sent first to France, where he had an affair with his doctor's wife, and then to a sanatorium in Madrid staffed by novitiate nuns, where he lived from 1901 to 1903. In 1911 and 1912, he wrote many erotic poems depicting romps with numerous females in numerous locales. Some of them alluded to sex with novitiates who were nurses. Eventually, apparently, their mother superior discovered the activity and expelled him, although it will probably never be known for certain whether the depictions of sex with novitiates were truth or fantasy.

In 1913, he met and fell in love with Zenobia Camprubí, a noted translator of the Bengali writer, Rabindranath Tagore. Shortly thereafter, he published a book of mildly erotic poems and made plans to publish the franker ones. But he abandoned his intention when Zenobia reacted to the first erotic book with disgust and ire.

The remaining erotic poems were to remain secret until 2007, when about a hundred of them were published under the title, Libros de amor (Books of love). In the description by the book's editor, "without abandoning his profound lyricism and transcedence, Juan Ramón here reflects a very explicit eroticism and sexuality which were alien to the time and concretely to Spanish lyric poetry".

The main subjects of many of his other poems were music and color, which, at times, he compared to love or lust.

He celebrated his home region in his prose poem about a writer and his donkey called Platero y Yo (1914). In 1916 he and Zenobia got married in the United States. Zenobia became his indispensable companion and collaborator.

Upon the outbreak of the Spanish Civil War, he and Zenobia went into exile in Cuba, the United States, and Puerto Rico, where he settled in 1946. Jiménez was hospitalized for eight months due to another deep depression. He later became a Professor of Spanish Language and Literature at the University of Maryland, College Park. The university later named a building on campus and a living-and-learning writing program in his honor.

In 1956, he received the Nobel Prize in Literature; three days later, his wife died of ovarian cancer. Jiménez never got over this loss, and he died two years afterwards, on 29 May 1958, in the same clinic where his wife had died. Both of them are buried in Spain.

Although he was primarily a poet, Jiménez' prose work Platero y yo (1917; "Platero and I") sold well in Latin America, and in translation won him popularity in the USA. He also collaborated with his wife in the translation of the Irish playwright John Millington Synge's Riders to the Sea (1920). His poetic output during his life was immense. Among his better known works are Sonetos espirituales 1914—1916 (1916; “Spiritual Sonnets, 1914—15”), Piedra y cielo (1919; “Stones and Sky”), Poesía, en verso, 1917—1923 (1923), Poesía en prosa y verso (1932; “Poetry in Prose and Verse”), Voces de mi copla (1945; “Voices of My Song”), and Animal de fondo (1947; “Animal at Bottom”). A collection of 300 poems (1903—53) in English translation by Eloise Roach was published in 1962.

His literary influence on Puerto Rican writers strongly marks the works of Giannina Braschi, René Marqués, and Manuel Ramos Otero.

The name of Juan Ramón Jiménez is familiar to students at the University of Maryland, the language building of which is named for the poet.