The biography of a “repellent” Italian poet and politician has picked up this year’s Samuel Johnson Prize for Non-Fiction beating Charles Moore’s biography of Margaret Thatcher.

The £20,000 prize was awarded to Lucy Hughes-Hallett this evening for The Pike, which chronicles the life of Gabriele D’Annunzio.

The judges for the UK’s most prestigious non-fiction prize, celebrating its 15 anniversary, said The Pike “transcends the convention of biography”.

Ms Hughes-Hallett has written a book on Cleopatra which won the Fawcett Prize and the Emily Toth Award, and is a fellow of the Royal Society of Literature

Her work beat Moore’s Margaret Thatcher: The Authorised Biography, Volume One: Not for Turning and Return of a King: The Battle for Afghanistan by William Dalrymple.

The rest of the shortlist comprised Charlotte Higgins’ Under Another Sky, A Sting in The Tale by Dave Goulson and David Crane’s Empires of the Dead: How One Man’s Vision Led to the Creation of WW1’s War Graves.

The winning work followed the “dangerously charismatic” D’Annunzio as he journeyed from idealist romantic poetry to radical right-wing revolutionary and national hero.

Martin Rees, Astronomer Royal and chair of the judges, praised the author’s “writing and her intricate crafting of the narrative”.

He continued that readers would be “transfixed by her vivid portrayal of D’Annunzio; how this repellent egotist quickly gained literary celebrity” and how his oratory influenced Italy’s involvement in the First World War and the rise of Mussolini.

The judging panel also included classicist Mary Beard, Shami Chakrabarti, director of Liberty, historian Peter Hennessy and writer James McConnachie.

Last year the prize was won by Wade Davis for Into the Silence: The Great War, Mallory and the Conquest of Everest. Past winners include Antony Beevor for Stalingrad and 1599: A Year in the Life of William Shakespeare by James Shapiro.