"Show up at the desk" is one of the first rules of writing, but for Wolf Hall I was about 30 years late. When I began writing, in the 1970s, I thought of myself simply as a historical novelist; I can't do plots, I thought, so I will let history do them for me. I had an idea that, after the French revolution was done and dusted, Thomas Cromwell might be the next job. Blacksmith's boy to Earl of Essex – how did he do it? The story seemed irresistible. I thought someone else would write it.

The 500th anniversary of Henry VIII's accession fell in 2009. Dimly aware of this, but not yet focused, in 2005 I proposed to my publisher a novel – just one, mind – about his great minister. Still no one had told the story. The Tudor scholar GR Elton had established Cromwell as a statesman of the first rank, but Elton's work had done nothing for his popular image. Holbein's portrait shows a man of undistinguished ugliness, with a hard, flat, sceptical eye. In A Man for All Seasons, he is the villain who casually holds another man's hand in a candle flame.

Biographies of him are cut up into topics: "Finance", "Religion" and so on. He seemed not to have a private life. It wasn't that I wanted to rehabilitate him. I do not run a Priory clinic for the dead. Rather, I was driven by powerful curiosity. If a villain, an interesting villain, yes? My first explorations challenged my easy prejudices. Some readers think I've been too easy on Cromwell. In fact it's possible to write a version of his career in which he is, at worst, the loyal servant of a bad master.

The deaths of Thomas More and Anne Boleyn can be laid at the king's door. In the end, this was not the story I chose to write. In my interpretation, Cromwell is an arch-plotter, smarter than Henry though not meaner. He had plenty "stomach", said his contemporaries: not a reference to his embonpoint, but to his appetite for whatever life threw at him. He was, as John Foxe said, "given to enterprise great matters". New wives, new laws, the split with Rome, the reformation of the church, the filling of the exchequer: there seemed no limit to his massive, imperturbable competence.

When I sat down to write at last, it was with relish for his company. The title arrived before a word was written: Wolf Hall, besides being the home of the Seymour family, seemed an apt name for wherever Henry's court resided. But I had no idea what the book would be like, how it would sound. I could see it, rather than hear it: a slow swirling backdrop of jewelled black and gold, a dark glitter at the corner of my eye. I woke one morning with some words in my head: "So now get up." It took a while to work out that this was not an order to get the day under way. It was the first sentence of my novel.

Wolf Hall attempts to duplicate not the historian's chronology but the way memory works: in leaps, loops, flashes. The basic decision about the book was taken seconds before I began writing. "So now get up": the person on the ground was Cromwell and the camera was behind his eyes.

The events were happening now, in the present tense, unfolding as I watched, and what followed would be filtered through the main character's sensibility. He seemed to be occupying the same physical space as me, with a slight ghostly overlap. It didn't make sense to call him "Cromwell", as if he were somewhere across the room. I called him "he". This device, though hardly of Joycean complexity, was not universally popular. Most readers caught on quickly. Those who didn't, complained.

After I had written the first page I was flooded by exhilaration. I am usually protective of my work, not showing it to anyone until it has been redrafted and polished. But I would have liked to walk around with an idiot grin, saying to the world: "Do you want to see my first page?" Soon the complexity of the material began to unfold. So many interpretations, so many choices, so much detail to be sifted, so much material: but then, suddenly, no material, only history's silences, erasures. Until a late stage, what would become a trilogy was still one book. It was only when I began to explore the contest between Thomas Cromwell and Thomas More that I realised I was writing the climax of a novel, not merely another chapter. The facts of history are plain enough, but the shape of the drama was late to emerge, and the triple structure later still. In my mind, the trilogy remains one long project, with its flickering patterns of light and dark, its mirrors and shadows. What I wanted to create is a story that reflects but never repeats, a sense of history listening and talking to itself.

• John Mullan will be talking to Hilary Mantel about Wolf Hall and Bring Up the Bodies at Drapers' Hall, London on 11 December. The event is sold out, but will be podcast.