Composed of long swooping lines, in his sharply cut coat, Benjamin Clementine resembles an art deco illustration of himself. He is balanced atop a high stool, stretched, bowed and arched over his grand piano, whose lower registers his fingers inhabit. When he opens his mouth, it’s either to speak with audible reluctance or to sing as if all the world depended on it.

Once down and out in Paris and London, Benjamin Clementine now fills churches with the newly reverential, attracting the type of heckler who tells him what a privilege it is to see him. He was already on the up when he won the Mercury prize last month with his extraordinary debut album, At Least for Now.

It is rare for a work to be so obvious in its sources yet so richly original. His music and his manner are overwhelmingly reminiscent of Nina Simone. Anyone can cop a style, but Clementine manages to delve down to her level of resonance, rapture and sorrow. He also recalls Antony Hegarty and Nick Drake, whose River Man he covers tonight. Yet his intense songs, autobiographical and elliptical as they are, could not conceivably be anyone else’s.

The album owes its remarkable texture to capturing the deep stillness between its sounds. Live, the songs are rougher and more frayed around the edges, and filled with compressed energy that intermittently blazes outwards like solar flares. Clementine performs either solo at his piano or accompanied by drums, which at first seem in clattering contest with him: at the end of Nemesis, he and drummer Alexis Bossard stand and incline gravely towards one another, as if they were judokas concluding their bout.

Clementine’s billowing voice is astonishing, but it is harnessed always to the feeling, the moment, and never runs off on its own path. The Mercury panel haven’t only given Clementine a well-deserved boost; they’ve done the rest of us a real service.

• At St John at Hackney church, London, on 7 December. Box office: 020-8985 5374.