In the autumn of 1792, a few months after Louis XVI’s overthrow, the historian, geographer and ex-priest Jean-Louis Soulavie arrived at the abandoned palace of Versailles with official permission to examine the former king’s archives. In the library on the fourth floor of the royal apartments, just below the smithy where Louis indulged his hobby of making locks, Soulavie found a mass of precious papers, including Louis’s correspondence with his ministers and agents and perhaps even a secret political diary. Nine years later, a few of these documents found their way into Soulavie’s six-volume history of Louis’s reign, the first ever published. The rest, however, disappeared, the result of hurried auctions and straightforward theft during the Terror. Filling this gap is the major challenge faced by Louis XVI’s biographers.

Another problem is one of the king’s own making. Louis XVI raised taciturnity to an art form. Before 1789, this had been a tactic to prevent pressure from his ministers, and during the Revolution it became necessary for his personal safety. Shortly before his death, he even remarked, ‘I would rather let people interpret my silence than my words.’ Ironically, when he did address some last words to his people at his execution, they were drowned out by a drumroll and only half a sentence was heard.

Bringing to life such an enigmatic and elusive character is a formidable task. John Hardman accomplishes this with immense subtlety and skill. He has already written one excellent biography of Louis, which appeared on the bicentenary of the king’s death in 1993. His latest, however, is greatly expanded: broader in scope and considerably more detailed. There are two reasons for this. The first is that, finally, some of the papers examined by Soulavie have resurfaced – 171 of Louis’s letters to his long-serving foreign minister Vergennes, which at a stroke quadruple the existing number. These were published in 1998. The second is that, after a long period of neglect, historians have returned to the field of 18th-century French politics and some important new works have appeared. The materials are now in place for a fuller portrait of Louis XVI than at any previous time.

As a result, Hardman is able to dispel many of the myths that have gathered about the king since his death. Contrary to what hostile contemporaries, echoed by many historians, claimed, Louis was very far from stupid or lazy. He was gifted at mathematics and geography, and fascinated by the sea – his reign saw a remarkable rebuilding of the French navy. He also spoke Latin, Italian and, surprisingly, English, the language of France’s hereditary enemy. Throughout his life he was alternately fascinated and repelled by Britain’s political system and commercial power. He is probably the only French ruler to have had a subscription to The Spectator. Louis’s flaw was not stupidity but sometimes paralysing indecision, a product of heredity, early bereavements and the stultifying ritual of Versailles. Its effects were memorably summarised by his younger brother, the future Louis XVIII: ‘Imagine a set of oiled billiard-balls that you vainly try to hold together.’

This indecision, however, was much less apparent before than after 1789. Indeed, the greatest importance of the newly available letters to Vergennes is in showing how effective Louis could be, particularly in foreign policy, the traditional business of kingship, when seconded by a minister he trusted. This is clearest in Louis’s most crucial decision before the Revolution, to intervene on the side of the Americans in their struggle against Britain. This had enormous consequences: it brought the United States into being but saddled France with a war debt that four years later pitched the monarchy into terminal financial crisis. Louis later claimed that he regretted the decision. In the course of eighty fascinating pages that shed much new light on this turning point in the American War of Independence, Hardman shows that ultimate responsibility was the king’s.

The next crucial question that Hardman tackles is that of Louis XVI’s attitude to the French Revolution. Here again, the problem of sources resurfaces. This time it can be traced directly to the king: in the days before the crowd stormed his Paris residence, the Tuileries, and dethroned him in August 1792, he ordered bonfires to be made of compromising documents in the palace courtyard. As a result, a central mystery remains about Louis’s policy after 1789: was he to any extent prepared to compromise with the Revolution, or was he secretly determined to crush it, by force if necessary, and restore the old regime? On the sparse evidence available, historians have come to sharply differing conclusions, with the majority arguing that he was unwilling to make any real concessions. Hardman, however, is convinced that Louis was in fact willing to do so, at least during the Revolution’s first two years, until its growing radicalism alienated him. For Hardman, the king was genuinely prepared to act as a constitutional monarch in partnership with the revolutionary National Assembly, provided that certain royal prerogatives were retained.

The problem with testing this hypothesis is that, three months into the Revolution, Louis and his family became virtual prisoners of the people of Paris, so from then on he was unable to express his opinions freely. This is why the ‘flight to Varennes’, the royal family’s dramatic escape attempt from Paris in June 1791, is so important – it was the moment during the Revolution when Louis came closest to being able to proclaim his true feelings about it. The evidence for what the king actually planned to do had the escape succeeded is – once again – fragmentary, but it has recently been re-examined and become a subject of lively debate. Hardman argues that Louis’s intention in leaving Paris was simply to find a place of safety from which to negotiate openly with the revolutionaries, rather than fight them. I am more sceptical. Had the flight to Varennes succeeded, the two dominating influences on the king would have been his wife, Marie Antoinette, and his ‘prime minister designate’, the baron de Breteuil, neither of whom had any intention of compromising. The likely result of the royal family reaching safety would have been civil war, which generally inclines no participant to moderation.

John Hardman sheds much light on the enigma of Louis XVI’s attitude to the French Revolution, but in the current state of research this problem cannot be fully resolved, and perhaps it never will be. His achievement is to provide an up-to-date, immensely erudite and compelling study, the fruit of a lifetime’s work on the king. It is also crisply, sometimes brilliantly, written. Hardman’s style is accessible, often witty, and he has a gift for putting complex issues in a nutshell. Louis XVI remains one of the crucial characters in modern history – as much for what he did not do as for what he did – and this is now the best biography of him in any language.