Javier Marías, who has died aged 70 of a lung condition, was widely recognised as Spain’s greatest contemporary novelist. His work, which included 16 novels, three volumes of short stories and several collections of his newspaper articles, has been translated into 44 languages and has, altogether, sold nearly 9m copies worldwide.

Marías’ constant themes – in novels such as Corazón tan blanco (A Heart So White, 1992) and Los enamoramientos (The Infatuations, 2011) – were secrets and betrayal, the latter coming perhaps from his father’s experience in the civil war, when – as described in Marías’s spy trilogy, Tu Rostro Mañana (Your Face Tomorrow, 2002-07) – he was betrayed by his best friend.

Marías also wrote movingly about old age, and cast an unflinching eye on male-female relationships. The novels often begin with a shocking scene – an unexplained suicide, the sudden death in bed of a lover, a complex love triangle – plunging reader and narrator into the plot-to-be.

The main characters are often translators or interpreters – or, latterly, spies – people who have renounced their own voices, but who are also, in a sense, interpreters of people, which is, of course, precisely what any good novelist aspires to be. In Your Face Tomorrow, the narrator, Deza, is recruited to become exactly that, “an interpreter of people”, whose job it is to write detailed reports on the people he has seen only in videos or via a two-way mirror.

Marías was also a notable translator, believing translation to be the best possible apprenticeship for a writer. He translated, among others, Thomas Hardy, Robert Louis Stevenson, Thomas Browne and Isak Dinesen; his version of Laurence Sterne’s Tristram Shandy won a national Spanish translation prize in 1979. He was a great anglophile and lover of Shakespeare, and several of his books – A Heart So White, Dark Back of Time (Negra espalda del tiempo, 1998), Tomorrow in the Battle Think on Me (Mañana en la batalla piensa en mí, 1994), Thus Bad Begins (Así empieza lo malo, 2014) – take their titles from Shakespeare plays, and abound in Shakespearean references.

His sentences are long and winding, much like those of Proust and Henry James, following the sinuous flow of a thought, always searching for the most precise way to express a complex, possibly contradictory idea. I was fortunate enough to be Marías’s main translator for 30 years. I would translate his books sentence by sentence (each sentence could sometimes be a page or more long) and took pleasure in rearranging the sentence to suit English syntax, while never losing the original thread or rhythm, and guiding the reader safely to the end, just as Marías did in Spanish.

He was also very funny. In A Heart So White, the narrator, another interpreter, wilfully mistranslates the words of a British politician who bears a striking resemblance to Margaret Thatcher. In The Infatuations, a mediocre writer is so convinced he will one day win the Nobel prize that he has already written his acceptance speech in execrable Swedish.

Born in the Chamberí district of Madrid, to Julián Marías, a philosopher, and Dolores Franco Manera, a teacher, writer and translator, Javier was the youngest of five sons. His father was briefly imprisoned by Franco’s Nationalists, and, on his release, was unable to take up a post at a Spanish university because he refused to swear allegiance to the so-called fundamental principles put in place by the Franco regime.

Fortunately, he received invitations to teach at Harvard, Yale and Wellesley College in the US, where the whole family spent the academic year when Marías was just one and, later, when he was four. Back in Madrid, Marías was educated at the liberal (and secular) Colegio Estudio.

He wrote his first novel, Los dominios del lobo (The Domains of the Wolf, 1971), aged 17, after running away to Paris. His friend and mentor, the novelist Juan Benet, found a publisher for that first novel, which was swiftly followed by Travesía del horizonte (Voyage Along the Horizon, 1973), written while Marías was at the Complutense University in Madrid, where he studied English literature.

Following graduation in 1973, Marías took a break from writing to focus on translation. From 1983 to 1985 he taught Spanish literature and translation theory at Oxford University, spending a term at Wellesley in 1984. From 1987 to 1992, he taught translation theory at his alma mater, the Complutense University.

His Oxford experience provided the basis for his 1988 novel Todas las almas (All Souls), the first of his novels to be translated into English. One of the minor characters in the book was the real-life writer, poet and anthologist John Gawsworth, who, as MP Shiel’s literary executor, inherited the throne of the non-existent Kingdom of Redonda, styling himself Juan I. In 1970, the independent publisher Jon Wynne-Tyson became Gawsworth’s literary executor, thus becoming Juan II, but, on reading All Souls, he abdicated in favour of Marías, who became Xavier I. Marías used his status as king to bestow mock-titles on friends and others he admired: for example, William Boyd became the Duke of Brazzaville and John Ashbery the Duke of Convexo.

In 2000, with Carme López Mercader, he set up a publishing imprint called Reino de Redonda, which specialised in translations (often by Marías himself) of neglected works such as Charlotte Riddell’s ghost stories (Marías was a fan of ghost stories), the film director Michael Powell’s only novel, A Waiting Game, and Joseph Conrad’s The Mirror of the Sea.

A Heart So White’s huge critical success, both in Spain and abroad – bringing him, among other prizes, the 1997 Dublin IMPAC award – allowed him to devote himself exclusively to writing, alongside his regular columns for various Spanish papers, which he continued to write until last month.

Marías was distinctly unmodern in some respects. He never used a computer (latterly his friend and assistant Mercedes López-Ballesteros fielded emails for him) and always wrote on an electric typewriter, correcting on paper, then retyping. The women in his novels all wear skirts and high heels, and everyone smokes.

His weekly column in El País often raised hackles, and he loathed kneejerk political correctness, but he was always on the side of the truth and true to his own beliefs.

Needless to say, he won countless prizes and, in 2006, was elected a member of the Real Academia Española. His last novel, Tomás Nevinson, will be published in English next year.

He is survived by Carme López Mercader, his long-term partner whom he married in 2018, and by three of his brothers, Fernando, Miguel and Álvaro.

• Javier Marías Franco, writer, translator and publisher, born 20 September 1951; died 11 September 2022