It is written as a lifelong series of journals kept by the fictional character Mountstuart, a writer whose life (1906–1991) spanned the defining episodes of the 20th century, crossed several continents and included a convoluted sequence of relationships and literary endeavours.

Boyd uses the diary form to explore how public events impinge on individual consciousness, so that Mountstuart's journal alludes almost casually to the war, the death of a prime minister, or the abdication of the king.

Mountstuart appeared in Boyd's short story "Hôtel des Voyageurs" written in the early 1990s and published in London Magazine and his 1995 collection The Destiny of Nathalie 'X'.

Biographer, belletrist, editor, failed novelist, he was perhaps most successful at happening to be in the right place at the right time during most of the century, and his journal – a huge, copious document – will probably prove his lasting memorial.Boyd distinguished journal, biography and memoir as literary forms, different treatments of the same essential subject, the human condition, the change in medium justified his writing again of a whole-life view: "I don't think there's anything wrong with going back over territory you've previously covered.

The first phase of Any Human Heart took 30 months as he carefully plotted Mountstuart's life to be significant but seem random, a period during which he bought several hundred books.

A short preface (an anonymous editor suggests it was written in 1987) explains that the earliest pages have been lost, and recounts briefly Mountstuart's childhood in Montevideo, Uruguay, before he moves to England aged seven with his English father and Uruguayan mother.

Logan is to get on to the school's first XV rugby team; Peter Scabius has to seduce Tess, a local farmer's daughter; and Ben Leeping, a lapsed Jew, has to convert to Roman Catholicism.

He embarks on a series of amorous encounters: he loses his virginity to Tess, is rejected by Land Fothergill whom he met at Oxford, and marries Lottie, an Earl's daughter.

Just before he departs for Barcelona to report on the Spanish Civil War, Lottie unexpectedly visits his London flat and quickly realises another woman lives with him.

He returns to Paris to finish his existentialist novella, The Villa by the Lake, staying with his old friend Ben Leeping (now a successful gallery owner).

Mountstuart mildly prospers in the art scene of the 1960s, meeting artists like Willem de Kooning (whom he admires) and Jackson Pollock (whom he does not); he moves in with an American lawyer, Alannah, and her two young daughters.

To boost his income and publicise the state of hospitals, he joins the Socialist Patients' Kollective (SPK), which turns out to be a cell of the Baader-Meinhof Gang.

In Any Human Heart, Boyd uses the journal form as a fresh angle from which to pursue the subject: "I wanted to invent my own exemplary figure who could seem almost as real as the real ones and whose life followed a similar pattern: boarding school, university, Paris in the 20s, the rise of Fascism, war, post-war neglect, disillusion, increasing decrepitude, and so on—a long, varied and rackety life that covered most of the century.

[8] John Mullan found the conceit most effective during the New York journal, where Boyd satirises figures in the Abstract Expressionist movement during the 1950s "whose characters seem almost beyond invention.

[8] An additional stylistic feature is the anonymous editor (Boyd), who introduces the book and offers explanatory footnotes, cross-references and attempts at dating.

[14] Richard Eder praised Any Human Heart in the New York Times: "William Boyd, is multifaceted and inventive, and he plays a deep game under his agile card tricks.

[16] In The Observer, Tim Adams complimented the opening sections as "nicely layered with the pretensions of a particular precocious kind of student" but criticised the "predictability" of Mountstuart's "walk-on part in literary history" and ultimately the suspension of disbelief, particularly the Baader-Meinhoff passages, concluding "For all the incident, for all the change he witnesses, Mountstuart never really feels like a credible witness either to history or emotion.

"[3] Giles Foden, in The Guardian, found the New York art-scene sections weakest, saying they "puncture the realism Boyd has so carefully built up in the rest of the novel.

"[5] Michiko Kakutani agreed that Mountstuart's youth was well evoked, but that the description of his retirement and poverty was "as carefully observed and emotionally resonant".

[18] While in the early part of the book "the characters' marionette strings [are] carefully hidden", later Boyd tried to play God, resulting in "an increasingly contrived narrative that begins to strain our credulity.

Several French newspapers favourably reviewed Any Human Heart, published in France in 2002 as "A livre ouvert: Les carnets intimes de Logan Mountstuart.

"[21] In France the book won the 2003 Prix Jean Monnet de Littérature Européenne[22] which rewards European authors for work written or translated into French.

Boyd wrote the screenplay, with (successively) Sam Claflin, Matthew Macfadyen and Jim Broadbent playing Mountstuart as he ages.

[26] The drama was broadcast in re-edited form as three one-and-a-half-hour episodes on 13, 20 and 27 February 2011 in the United States on PBS as part of the Masterpiece Classic program.