“Sent from heaven to finish all your educations” was how Walter Sickert defined himself in 1907 to young British artists. Aged 47, he had just completed his own education: a decade living between Dieppe and Venice, exhibiting in Paris, honing influences from his mentors, Whistler and Degas, before detonating European modernism in a domestic context — the Camden Town nudes.

Set in north London’s grim bedsitter-land, where sex worker Emily Dimmock was murdered in 1907, these are so dark and claustrophobic, the figures splayed close-up on dizzyingly angled iron beds, that Sickert was — still occasionally is — suggested as Jack the Ripper. That is nonsense, but at Tate Britain’s retrospective, the analogy between paint and violence is incontestable: rough impasto surfaces, bruised blue-grey tonality, smudgy marks creating an uneasy mood.

“La Hollandaise”, monumental with huge thigh and sagging breast, has for a face a mere slashing brushstroke, features destroyed, unreadable. Threatening, clothed men loom in the shadows above the ungainly curled-up nude in “L’Affaire de Camden Town”, and the corpse-pale torso with bloodied head in “The Camden Town Murder”. “Woman Washing Her Hair” is a voyeur’s picture — we see bent over a tub only a headless, emaciated body, “thinnest of the thin like a little eel,” Sickert said.

In Parisian terms, Sickert’s nudes were hardly radical — Picasso was already a cubist — but they are more compelling, disturbing and fiercer than anything in the preceding half-century of Victorian and Edwardian painting.

Tate displays the group in brilliant context. Sickert looks back to Degas’ blurred contours, contorted poses and discomforting angled spaces, as in the scintillating “Après le bain, femme nue couchée”, and to Bonnard’s voluptuous sinuosities and tipped interiors in the smoky “Femme nue sur un lit”. He anticipates, too: Lucian Freud’s paint-as-flesh in the awkward nude on a brass bedstead “Naked Portrait”.

Cosmopolitan and polyglot, born in Munich in 1860, brought up in London, Sickert fell naturally into the role of modernism’s go-between, connecting Europe and Britain, aestheticism and popular culture, painterly painting and narrative realism.

His instinct for the anecdotal — “I have always been a literary painter” — collided with late-19th-century avant garde insistence on pictorial artifice, derived from Manet and felt, by Sickert, through apprenticeship to Whistler. Sickert sought greater firmness than Whistler’s hazy effects, but mysterious atmospheres remain the hallmark uniting his immensely diverse (and uneven) work here.

A gathering of self-portraits shows an artist experimenting ceaselessly with identities. Sickert’s first career was as an actor, and a closely worked linear drawing, head thrusting forward, mobile features, suggests ambitious self-presentation as early as 1882. By the mid-1890s, in a sombre palette, he is gaunt, depressive, following a failed marriage and stalling career. He returns in 1907 with “The Painter in his Studio”, a game of mirrors and changing viewpoints, and the sharp-eyed, stylishly dressed “Self-Portrait: Juvenile Lead” — determined to shape a generation.

“Self-portrait: The Bust of Tom Sayers”, standing between a popular boxer’s bulky statue and a delicate porcelain vase reminiscent of Whistler, celebrates conflicting interests. “Self-portrait: Lazarus Breaks his Fast” is a comedy of an old man guzzling cereal. Taking another biblical persona, in “The Servant of Abraham” he compresses a larger-than-life, sketchy, monochrome face, with glowing outline, into a small canvas, backlit, cropped, based on a photograph, and ambivalent — defiant, grim, vulnerable.

Unsurprisingly, the two subjects which established Sickert’s reputation were theatrical. He began depicting music halls, and with their mirrored interiors he transferred Whistlerian magic of light and space to plebeian urban settings. Tate’s poster image is “Little Dot Hetherington at the Bedford Music Hall”: a child singer in frothy white — cousin of Degas’ ballerinas — seen in reflection. It fizzes with the nervous energy of performance, the play of multiple perspectives, spatial ambiguity.

In “The P.S. Wings in the O.P. Mirror” stage left and right (prompt and opposite prompt side) are mirrored, creating a bizarre scenography where singer, in bright red, and audience face in opposite directions. The cropped, tilting “Gallery of the Old Bedford” gives the vertiginous sense that the wide-eyed youths in the “gods” are about to tumble over the theatre’s ornamental curving balconies.

Sickert could paint like a jeweller, and his intricate, encrusted surfaces became yet richer when, seeking renewal, he chose Venice — the city as stage set. Depicted in thin washes over crisp, calligraphic drawing, his 1896 trio of St Marks’s facade, its crosses, spires and mosaics tinged pink or emerald or gold according to time of day, and the nocturne “The Horses of St Mark’s”, recall his glitzy, gaudy music hall interiors. They are also bang up to date — an influence is Monet’s groundbreaking 1895 “Rouen Cathedral” series.

It is unfortunate that this show, arranged by subject (portraits, places, theatre pieces), works against a tracing of Sickert’s development, for Venice fascinatingly yet unpredictably shaped the rest of his oeuvre. During bad weather in 1903-04, he painted sex workers La Giuseppina and Carolina dell’Acqua, bored and sultry, in oppressive interiors. “Two Women on a Sofa”, subtitled “Le Tose”, Venetian slang for girls, blurs faces while concentrating on expressive poses. In “Fille Vénitienne Allongée” one girl sprawls in a négligée, legs apart; the other, headless, perches beside her. The sinister two-figure Camden pictures are a breath away.

So is Sickert’s most famous composition, “Ennui” (1914), all kitchen-sink dull browns and beiges: “The old publican with his glass on the table . . . and a cigar gone cold at his lips, looking out of his shrewd little pig’s eyes at the intolerable wastes of desolation in front of him,” as Virginia Woolf described, while “a fat woman lounges, her arm on a cheap yellow chest of drawers, behind him.” 

For Woolf, Sickert was “a novelist — realist of course”. But a year after “Ennui”, in “Brighton Pierrots”, his greatest painting, he bursts into ecstatic, unreal chromatic harmony, redolent of his Venetian colours: performers, seafront houses, deckchairs, all pinks and acid greens beneath a twilit sky clashing with illumination from phosphorescent spotlights. The entertainers, disproportionately large, face a war-depleted audience: though strange and melancholy, their show, analogy for the joy and artifice of painting, goes on.

Sickert went on, through the 1920s and 1930s, creating queasy, washed-out portraits modelled on snapshots, of wildly varying quality yet heralding post-1960s photo-based painting. The best, another rose-emerald pattern featuring actress Peggy Ashcroft on Venice’s Accademia Bridge, is inexplicably excluded (owned by Tate, it will feature in the show’s Paris iteration).

At Tate’s 1960 centennial retrospective, David Sylvester complained that Sickert “was thoroughly English in his lack of single-mindedness”, unable to carry ideas “to an extreme conclusion which is achieved by every great artist”. The contrasts here with Degas make the point, but the 21st century is more forgiving: Sickert, hybrid, uncertain, painting loose and free, is our contemporary.

Tate Britain, London, April 28-September 18, tate.org.uk
Petit Palais, Paris, October 14-January 29, petitpalais.paris.fr