Cardinal Newman said not to trust a recent convert.

I am a late convert to the writings of Penelope Fitzgerald, who died in 2000. I came to her fiction only recently while reading a heap of post-1980 English writers in order to update A History Of English Literature. I have since read or re-read Fitzgerald's 15 published books: three biographies, nine short novels and a volume each of short stories, essays and letters. This has confirmed my impression that she was the most remarkable English writer of the last quarter of her century, not only for the quality of her writing, but also for its human understanding and its range.

Professor Hermione Lee's life of Virginia Woolf met with Fitzgerald's approval. Lee now writes the life of a writer whose novels have a richer humanity and more substance than those of Virginia Woolf.

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This biography is written with the co-operation of the writer's children, and with full access to the relevant papers. It is clear in structure, thorough in coverage, and acute and helpful on the novels. It may be supplemented but will not be replaced. Fitzgerald's own approach to biography was selective. Her biographer documents a long and unusual life, full of surprises. Simply put, it was a life of promise, disappointment, adversity, perseverance, belated achievement and final triumph.

Penelope Fitzgerald's story is, then, an encouraging one, and not only for writers. Things did not go well for her in the middle of her life, which may be why her first book - a life of the painter Edward Burne-Jones - appeared only in her 60th year. Her subsequent biographies, The Knox Brothers and Charlotte Mew And Her Friends are as rich and rewarding as any novel. But as she turned more to fiction, her novels became more carefully organised, and both graver and funnier.

She writes about mismatched love and the mishaps of life, though not in a miserable spirit. She uses the economy of comedy to deal with material which involves tragic surprises. She preferred, she said, not to insult the reader by explaining too much.

Offshore won the Booker Prize in 1979, but she never had a popular readership. Only with her last and most miraculous book, The Blue Flower, did she have a hit (in the US, not the UK) and make money. Frank Kermode, AS Byatt and Julian Barnes liked her books, but the sales reps found them hard to put across. It did not help on the promotional circuit to have been born in 1916, to favour William Morris pinafores and to be a lady. Interviewers found her modest, self-deprecating, elusive; some failed to notice the intellectual steel.

One of the things which Mrs Fitzgerald did not discuss was Mr Fitzgerald. Silence about strong personal emotion was a rule of her father's family, the Knoxes. Knoxes were bishops, linguists, missionaries, saints, translators of the Bible, intellectual sceptics, sharp writers of books. Chief sceptic was her uncle, the cerebral Dillwyn Knox, a Greek scholar and a leading cryptanalyst in both wars. Another uncle, Ronnie Knox, converted to mainstream Catholicism; his father (a bishop) disinherited him.

Penelope's father, EV Knox, the editor of Punch, could say important things only in asides. Shot in the back by a sniper at Passchendaele in 1917, he lived to be 90. His last reported words were: "There's an awkward thing about dying - one gets so little practice."

Fitzgerald's grandfathers were bishops. Her mother was one of the first women to read English at Oxford University, where Penelope took a congratulatory First. When war broke out, she worked at the Ministry of Food and then in the BBC. She married Desmond Fitzgerald, an Oxford contemporary, who was a barrister and a soldier.

Desmond won a Military Cross in North Africa with the Irish Guards, and another medal in Italy, but he returned a changed man. They lived in Hampstead, had three children, and jointly edited World Review. It failed. Insolvent, they retreated to East Suffolk. They then lived on a barge off Chelsea, which sank. It sank for a second time in 1963, but by then Desmond had cashed cheques from his Chambers in local pubs. Disbarred, he lost friends. The family was homeless, destitute, declassée.

Penelope taught for 26 years in London crammers; she dyed her hair with tea-bags. Major Fitzgerald, MC, became a travel agent's clerk; he died of undiagnosed cancer in 1976, having spent the last 10 years of his life issuing travel tickets.

He had also helped his wife with her first books. And, held together by Penelope's fortitude and their own resolve, the family survived and slowly got back on its feet. The Fitzgerald children grew up to lead good and useful lives.

Fitzgerald's early novels, The Bookshop and Human Voices, draw on her own time in Suffolk and at the BBC. Her last four novels are not personal but historical: Innocence, set in 1950s Italy; The Beginning Of Spring in Moscow in 1913; The Gate Of Angels among Cambridge scientists in 1912; and The Blue Flower in provincial Germany at the time of the French Revolution. They are continually surprising, often astonishing works: the settings are entirely convincing, but by some mysterious mechanism the reader is made to feel a contemporary of the characters.

A rich and fascinating life, then, as we now know thanks to Hermione Lee, who allows us to trace its detail with understanding.