CANNES - If any critics were about to ding Mike Leigh for wading into the warm waters of the period prestige picture for his latest, long-contemplated feature, let it be known that the veteran writer-director has come prepared. "What is wrong with being a portrait painter?" asks a slighted practitioner of the form at an ego-crammed artists' gathering midway through "Mr. Turner," Leigh's expansive, exquisitely realized biography of Britain's foremost Romantic painter. The retort from a colleague is airy and sneery and entirely predictable: "What does it do to elevate the art?" he smugs. 

You might ask the same question, and receive the same answer, about the biopic genre -- routinely dismissed by highbrow critics as an easy-access route to bland, Oscar-gilded gravitas, subverted only by a few filmmakers resourceful enough to bend the form's rigid structure and insert something of themselves between the factual lines. Leigh earned his stripes as an exception with 1999's jubilant "Topsy-Turvy," which used a brief stage in the lives of musical theater giants Gilbert & Sullivan as a jumping-off point for a playful rumination on the trials and errors of creative collaboration.

In taking on the life of J.M.W. Turner, a very different, arguably more enduring contributor to the country's cultural fabric, Leigh is working on a grander canvas, seeing his subject through from his prime (professionally, if not personally) to his decayed deathbed. At 150 unhurried minutes, it's actually shorter than "Topsy-Turvy," but feels more muscular -- a sober affair, though often a mournfully funny one. And while the films cover some common thematic ground -- the artist's insecurity, the tension between pleasing oneself and an audience -- "Mr. Turner's" passions and neuroses feel more peculiar to Leigh and his own work. It's tempting, even, to view the film as biopic-as-self-portrait, revealing shades of one life through another. Leigh has a reputation for prickliness and resistance to self-explication; perhaps it's not surprising that he's long been fascinated by Turner's allegedly gruff, taciturn genius.

As played by Timothy Spall -- an erstwhile mainstay in Leigh's company now collaborating with the director for the first time in 12 years -- Turner could hardly be a more abstruse, less lovable figure. His weatherbeaten face fixed in a pout of sturgeon-like severity, Spall delivers his spare dialogue in a guttural, rumbling register that practically requires subtitles, whittling entire sentences' worth of information down to a single, pointed grunt. He weeps like a sea lion and shags like a rutting rhinoceros; when he coughs, which is often, his phlegm lands practically wet on the screen. It's a boldly animalistic performance, and one that will alienate any admirers who have previously imagined Turner as a figure rendered in his own rapturous brushstrokes. He is the beast to his art's beauty.

Leigh’s film is hardly the first biopic to stress the conflict in identity between an artist and their work, or at least the public understanding thereof -- though “Mr. Turner” keeps its subject’s spiritual drive and visual imagination something of a mystery to the end. It’s one of the few painter-focused films that doesn’t indulge in stock scenes of its protagonist liberally dabbing oils across the canvas in an inspired fever; rarely, in fact, do we see Turner’s vast, ethereally lit landscapes and seascapes as works in progress. Leigh and his longtime cinematographer Dick Pope more often imply Turner’s vision through his surroundings, and not always the vistas he’s actually painting: his London studio, for example, is frequently bathed in the kind of lemon-meringue twilight that is immediately recognizable from Turner’s paintings, but rarely alights upon the English capital in real life.

As such, Leigh’s world-building is immaculate: abetted by Suzy Davies’ extraordinary production design, “Mr. Turner” subtly constructs environments -- be it the ship-speckled Margate coastline or the interior of an aristocrat’s drawing room -- that evoke what Turner sees, tonally and spatially, that those around him cannot. The honeyed, ambient abstraction of his painting “Sunrise With Sea Monsters,” when it appears, feels more or less of a piece with the film’s aesthetic, but horrifies onlookers: “A dirty yellow mess,” proclaims Queen Victoria, to the artist’s evident chagrin.

Leigh, not a filmmaker who has ever encountered much opposition from the critical majority, nonetheless makes a piqued, pointed statement here against that community’s rush to judgment, “There is no place for cynicism in the reviewing of art,” one character states with earnest aggrievement, while Leigh’s camera gazes adoringly enough at Turner’s famous finished canvases to drive home the point that they outlasted their critics, and then some. There’s something a little preening in the way “Mr. Turner” aligns itself so righteously with the master that’d be more aggravating if it didn’t feature some of the loveliest, most pristine filmmaking of Leigh’s career.

Spall’s deliberately distancing performance notwithstanding, “Mr. Turner” is easier to like when Turner’s personal life, rather than his artistic legacy, is in focus. His tentative romance with widowed boarding-house proprietor Sophia Booth (the wonderful Marion Bailey) is tenderly etched, delineating the gently rules of engagement between two self-sufficient souls unused to being loved, but stops just short of sentimentality: when he awkwardly comments on her beauty, she edges out of directly returning the compliment. As his loyal housekeeper Hannah, meanwhile, Dorothy Atkinson only reveals the depth of her feelings for her coarse, inattentive employer in gradual isolation. (Not all Leigh’s women are as well served: Ruth Sheen is a jarringly broad comic presence as the embittered, abandoned mother of Turner’s two equally sideswept daughters, while a wry Lesley Manville is sorely underused as Scottish scientist Mary Somerville.)

Neither a sprawling cradle-to-grave life study nor a disciplined examination of a specific creative stage, “Mr. Turner” unfolds with Leigh’s customarily discursive, episodic ease -- which will, as ever, frustrate some and delight many. It’s a robust film that could only have been made by an artist as practised and assured as his subject, which is not to say it’s complacent: just as Turner, in one of the film’s closing scenes, examines with curiosity the camera obscura that he fears will render his own gifts obsolete, Leigh too is examining more advanced areas of his craft, while remaining pretty confident of what he already knows.