Hester: The remarkable life of Dr Johnson's 'Dear Mistress', By Ian McIntyre

Samuel Johnson's friend, sparring partner and biographer could fill a dictionary of her own

When Johnson first went to dinner with her, in 1765, she was Hester Thrale. Her husband, Henry, was a philandering, fox-hunting MP and the owner of a lucrative brewery in his constituency, the Borough of Southwark. Dinner was at an insalubrious spot in Dead Man's Place, near a vinegar factory and the old Clink prison. The venerable lexicographer was easily the most important visitor ever to go there.

But the Thrales also owned a grand estate of 100 acres in rural Streatham and it was to this house that Mrs Thrale invited Johnson to stay, when it became clear that he was suffering from such a deep depression that he feared madness. For the first time since his childhood he became part of a family and was indulged. Here he could practise the verbal pugilism he so enjoyed, in which Hester was his most spirited sparring partner; here if he liked – and he often did – he could gorge on fresh peaches before breakfast. With her lively wit and warm affection she probably saved his life.

Their friendship lasted 16 years, during which time she was nearly always pregnant. Of more than a dozen children, only four survived. She had to be tough and pick herself up: when her daughter Penelope was born and died within 10 hours, she wrote: "Poor little maid!... one cannot grieve after her much and I have just now other things to think of."

When her husband died, it was widely supposed that Thrale would marry her children's "toy elephant", but instead she chose her children's Italian music master, Gabriel Piozzi, with whom she was extremely happy. She lived on into great old age, and celebrated her 80th birthday by opening a grand ball at 2am with Piozzi's nephew, whom she had adopted.

Those are the bare bones of a story into which Ian McIntyre breathes magnificent new life. He has a wealth of material, for Hester was, as she happily acknowledged, an inveterate scribbler. In 1776 she was pregnant for the 11th time when Henry came home sporting an enormous testicle, thus fulfilling her father's dying prediction. "If you marry that scoundrel," he had said, "he will catch the Pox, &, for your Amusement, set you to make his Pultices." As she did, "fomenting the elegant Ailment every Night and Morning for an Hour together on my Knees." Perhaps to make amends, he presented her with six blank quarto volumes, each bound and stamped with the title Thraliana. She filled them all, and she didn't stop there.

These books, and many more, are packed with stories, memories, anecdotes, gossip, poems and politics. The prodigiously precocious only child of impoverished but grandiose parents – "People of Strong Parts" she called them – she learned very early how to flatter and impress.

She used those necessary skills all her life, and never entertained the slightest doubt about her own abilities. She knew everyone, from Hogarth, Garrick and Reynolds to Bowdler, Fanny Burney and Sarah Siddons, and she made friends of most of them.

She had enemies, too – most notably Boswell, who couldn't cope with the fact that Johnson had actually liked her so well and who did his nasty best to blacken her character. McIntyre is her champion here, using an attractive combination of scholarship and sympathy to fight her corner against what he describes as Boswell's "lubricious maunderings". Her Anecdotes of the Life of Samuel Johnson he considers a better book than Boswell's celebrated biography: though darker in tone, it is more perceptive and less sentimental. McIntyre writes with a vigour and relish to match his subject's own and, although he is aware of her lapses from grace, like all the best biographers he sees as she saw, and is nearly always on her side.

Hester did not limit herself to writing about Johnson: she published a travel book, a book about English usage that might have inspired Fowler, and an extraordinary history book covering 1,800 years of Christendom. These were often disdainfully reviled for their anecdotal style but they were ahead of their time. Few of her contemporaries remain as readable.

She feels so contemporary to us. Again and again, she expresses views demanding an appreciative cheer. Exasperated with recalcitrant daughters, for example, she complains: "One's arms do so ache with pulling at an unbroken filly." It is glorious to see her so properly appreciated.