It is theoretically possible that future political leaders may take mistresses; such politicians might even love them. (Once we have an acceptable term for the male equivalent of "mistress", other than just the prosaic "lover", we can remove the sexist tinge to that proposition.) Nonetheless, no leader to come is likely to set up his mistress and their daughter in a separate, alternative family home, while keeping all those arrangements a state secret, well aware of the lethal political risks in disclosure. No such elected official would also maintain his wife in another house altogether, while strolling across a river into a presidential palace for work.

Nor can we expect the powers that be to write 1218 elegant, eloquent love letters over 33 years to their mistresses. No one has the requisite patience, passion or attention span any more. The debris of our time will be merely the static of emails, staccato text messages, silly emojis and succinct mobile phone conversations. Hillary Clinton made one pertinent comment in passing. She lamented the loss of brief conversations with voters when shaking hands on rope lines. Instead of disclosing their hopes and woes as they used to do, Clinton recalled, all the bystanders wanted to do now was to stage a selfie with her. For lovers, even gifts of flowers and chocolates might feel like a stretch these days. No one in power or anywhere close will write so much so well to their lover (of any sex or standing) ever again.

Let me explain the backstory, here, for Lettres à Anne ostentatiously explains nothing at all by way of introductory context or circumstance. The reader is invited to begin with the first letter. Frank Moorhouse once wrote a story titled Forty-Seventeen, but the initial disparity in age – and therefore experience, worldly wisdom, crisis management, moral conundrums and battle scars – between François Mitterrand and Anne Pingeot was wider than that, at 46 and 19. Mitterrand fell in love with Pingeot in 1962, at her parents' house, then remained devoted to her until his death in 1996. During all those 33 years, he remained married to his wife, Danielle, a tough-minded, politically dogmatic, somewhat stern woman who also had a private life of her own. As an extra layer of complication and controversy, Mitterrand served for 14 of those years as president of the French Republic. To insert one final twist in the tale, after striving for much of his life to gain the presidency, Mitterrand was diagnosed with cancer only a few months after being sworn in the first time, told then that he only had between three months and two years left to him.

To disclose an interest, I saw, listened to, read about and met Mitterrand in Paris. To an outsider whom the president had no need to flatter and a foreigner from a country about which he knew little, Mitterrand was just as he presents himself in the letters: wry, sly, deeply read, sharply intelligent, alert, curious and – as he tried so hard to be with Pingeot – seductive (entirely platonically, in my case). My favourite connection with Mitterrand is not chats but a more oblique, incidental link. In one letter, Mitterrand mentioned visiting a favourite bouquiniste (a bookseller with a stall by the Seine) to buy an edition of Pierre Drieu la Rochelle. I, too, cherished that weirdly compelling, refined fascist writer from between the wars. When I asked the same bounquiniste if he stocked any novels by Drieu, he quizzed me about which ones I wanted and why I intended to read them. Only after sincere answers did he consent to bring out from under his shelves a carton of interwar right-wing literature, noting that only one other customer had ever asked for Drieu's work, that other client being the president of the Republic.

Drieu is only one of dozens of writers whom Mitterrand commended to Pingeot. He starts off with François de La Rochefoucauld, gives her his first copy of a Stendhal and – rather obsessively – lists for her edification his preferred authors (as well as singers, past and present, composers, artists and so on). All that banging on might seem affected and pretentious, but I suspect that it reflected also the habits of a well-furnished, insatiably curious, intellectually consequent mind. Mind you, Mitterrand does seem to be looking not only for replies from Pingeot (always nagging when they arrived late) but also seeking a reflection or refraction of himself in her. He was too devious, too Florentine, too Byzantine, too French, to run one agenda alone. Mitterrand was writing to and for himself, as well as Pingeot. The critical element with his letters if that, for once, a past master at manipulation, dissimulation and tactical finesse might actually – by and large – be telling the truth. The one point Mitterrand repeated throughout the letters seems the most authentic of all: he frequently told Pingeot: "I love you."

Mitterrand was also too shrewd, too knowing, to rely on only one technique of seduction. His and Pingeot's daughter, writing as a 13-year-old, reminds the reader that her father was a "grand tombeur de femmes", as though women fell for him in the same way they "fall" pregnant". The letters therefore include five uses for a rose (later Mitterrand's political emblem); a smiley face (from 1964 onwards, as a sort of primitive emoji); a short prayer (however unlikely); a somewhat fussy, fumbling analysis of the state of grace; and lots of poems. Mitterrand outlined his remarkably tortuous task in January 1964: "how can you love a woman you only have half of, where you know only the image, behind the mirror of words and silences". How do I love thee, let me count the ways.

As for politics, evidently Mitterrand's true love, that avocation is often presented in the letters ironically, as though politics were a frustrating, fruitless digression from seduction. Letters from 1968 confirm again that Mitterrand lost the plot in that year of upheaval. "Esoteric verbiage" and "verbal sectarianism" are pungently condemned at one point, as Mitterrand again and again depicted politics as an interminable sequence of mundane, tedious meetings. In 1964, he did once concede that issues had become intense, "sometimes dramatic", but a reader might pine for more detail more often. None of the indiscretions about government secrets that distinguish H. H. Asquith's letters to Venetia Stanley (1913-15) appears here. A debate on China with Simone de Beauvoir, for instance, is simply remarked upon, rather than described.

The letters contain no hint of Mitterrand as a Winston Churchill, zealously rewriting history with himself as the sole hero. The correspondence does, however, remain one-sided, with no replies published and Pingeot confining herself to annotating her lover's text with a few asides (including one particularly waspish one, in 1970, about Mitterrand's reaction to her gaining social standing in her own right and independent means of support). She never plays Abigail to Mitterrand's version of John Adams.

Churchill won the Nobel prize, for literature. Mitterrand's laurels and legacy lie elsewhere, in his "grands travaux" (major new public buildings) like La Défense and the national library, and within a Socialist Party still entangled and enmeshed by his record. That said, the letters are a genuinely beautiful literary artefact. The French are inimitably themselves; one Paris reviewer complimented Mitterrand on his deft use of the past subjunctive. The letters deserve higher praise for their richly evocative sense of place (from a church hidden away high in the Morvan to Yamoussouko), and for Mitterrand's fascination with, in his own phrase, "the beauty of forms, of ideas, of perspectives". This correspondence comprises a kaleidoscope rather than a telescope, revealing all the intricacy, and eclectic eccentricity in Mitterrand's interests.

A large proportion of these letters were penned in the Senate and the National Assembly during parliamentary sessions (and how much time must Mitterrand have devoted to the task). When he moved into the Élysée Palace, the letters dried up. The year he was first elected produced only 11 lines of correspondence. His second family received lots of postcards, and plenty of affection in the flesh, but Mitterrand seemed too busy, too guarded, too distracted to write. Readers need to rely on the many volumes of Verbatim, which contain Jacques Attali's transcriptions of numerous Mitterrand's conversations. In those books, though, Mitterrand remains entrapped in what he called in a letter his "carapace ordinaire", his banal, day-to-day shell. He may have governed in prose, but certainly wrote letters to his mistress in poetry.

Mark Thomas is a Canberra-based writer. Lettres à Anne, by François Mitterrand, is published by Gallimard (October 2016).