Painting is a fight and few artists demonstrate this more emphatically than the volatile and complicated post-war master, Joan Eardley. Scotland’s great English artist or England’s great Scottish artist, box her as you will, she’s revered north of the border, but often oddly dismissed south of it. The Scottish public have been enthralled by her work for decades, and spoiled in their access to it, with 60 or so pieces in the National Galleries of Scotland collection alone (the Tate has just one). You’re rarely far from an Eardley here, and never more so than in this, her centenary year, which sees some 20 shows and events lined up to celebrate her life and work.

Only one of the exhibitions is in England, the country of Eardley’s birth. Visitors to the National Trust property at Mottisfont in Hampshire can enjoy three fine landscapes, but for the full Eardley experience explore Scotland (if allowed) and feast upon a rich, if scattered, display of drawing and painting from throughout her prolific but tragically short career.

Eardley died of cancer in 1963, at the age of just 43, but she left behind a prodigious quantity of portraits and landscapes, the best of which position her among the finest artists of her generation. Her Scotland is an emotional one, reflecting a challenging personal life, marked by deep depression, largely closeted lesbianism and punishing mood swings. A decade or so before her death, she wrote: ‘A terrible helpless, hopeless feeling has come upon me. Everything seems to be such a dreadful unending struggle.’ This state of mind characterised much of her adult life, and drove much of her best work.

Born in England to a Scottish mother and English father, Eardley experienced life-changing emotional trauma at the age of eight when her father killed himself and perhaps she never quite recovered. She grew up in suburban London but in her teens moved to Scotland with her mother, settling in the affluent Glasgow suburb of Bearsden.

Glasgow was to prove an inspiring place for the young Eardley. She trained at Glasgow School of Art where she learned to kick against the controlled finish and technical perfection usually expected of competent artists in 1940s Scotland. She fell in with a loose group of painters, including Bet Low and Tom MacDonald, who were drawn to the stylistically inventive social realism of Josef Herman and Jankel Adler, Polish refugees who had arrived in Glasgow in the early 1940s. They soon moved south, but not before leaving a profound and lasting impression on the young artists of the city.

Eardley sought her subjects not in leafy Bearsden but in the condemned slums of Townhead. She was fascinated by the families she met there, particularly the children, who she drew and painted obsessively. This was a hugely creative arena for Eardley, and we see her restlessly experimenting with technique in endless rapid portraits and tenement street scenes. For many Scottish viewers, works such as ‘Girl with a Poke of Chips’ (Scottish Gallery, 30 July – 28 August) capture a now popular image of the slums as messy havens of strong community and even stronger characters. For others, Eardley treads dangerously close to caricature and sentimentality, but there’s a raw, energetic honesty to her Glasgow pictures that largely elevates them above the mawkish.

Stylistically, these works are defined by strong drawing that simplifies and flattens form, and a muted palette interrupted by violent bursts of colour. Playing with collage and echoing the mark-making of chalked graffiti, Eardley recalls both cubism and the observant eye of the street photographer Brassaï, and she marries this with the characterful physical convolutions of Schiele. The result is a suite of drawings and paintings that are alive with childlike energy, and while there’s no denying that Eardley’s brand of social realism shies from the grimmer realities of slum life, it’s easy to see why the popularity of these playful works endures.

For me, though, the Glasgow pieces are just a prelude to the stuff that confirms Eardley as one of our greatest mid-century painters. The landscapes she produced around the village of Catterline during her final decade, paintings in which the emotional power of Turner meets the vigorous technique of abstract expressionism, represent a new level of turmoil, passion and brilliance.

Eardley came to Catterline, a straggle of cottages perched above the North Sea in Aberdeenshire, in 1951, at the age of 29. The location was to define the rest of her short life, offering both unquenchable creative inspiration and a refuge from Glasgow, where she felt socially ill at ease and professionally inadequate. She may have declared in a 1952 letter that ‘Being a lesbian itself isn’t a thing to worry me,’ but she also went on to say: ‘The trouble is that life hasn’t worked out well at all and so I’ve reached a state of most unholy muddle and my painting isn’t going well either… I just don’t believe in masterpieces coming out of misery.’

Fortunately, in Catterline, everything was about the painting and, miserable or not, she was finally able to produce her masterpieces. She abandoned portraiture, turning instead to the landscapes of her new environment. Here she moved her work on to another level, unleashing a ferocious body of hugely expressive, abstracted paintings that force the essence of the north-east coast, its weather, colours and textures, on to the board.

The Catterline works are instinctive, gestural paintings that grab the viewer and thrust them, face-first into the oncoming gale. Eardley’s landscapes are as much about feeling as seeing and, throughout her time in the north-east, they become progressively more daring, and more impressive. The real change comes when she finally tackles the sea, having strangely turned her back on it initially to focus on the inland views of cliffs, village and fields.

But finally, emboldened perhaps by a visit to a De Staël exhibition in Edinburgh, she turns around and looks to the ocean. Her surfaces, cheap hardboard left out in the rain to warp, become larger, as she needs more space to take on the never-ending expanse of the ocean. ‘Breaking Wave’ from 1960 (on show at the Hunterian from 30 July) encapsulates the bold new Eardley. It’s a perfectly balanced accumulation of earthy colours plus one defiant streak of blue, defined by sweeping, loose, drippy brushstrokes and, in the breaking wave, scrawly, painty drawing that harks back to those Glaswegian graffiti marks.

Eardley was always intensely driven and focused on becoming a better artist. But although her work was maturing and she seemed to be finding a profound voice, she remained riven by self-doubt and very critical of her own work. ‘I’ve been a bit down in the dumps about my bad painting lately,’ she wrote to a friend towards the end of her life. ‘It’s so hard to paint how you feel you want to.’ We see this struggle playing out in her paintings at this time. There’s a physical battle in progress, an attack on both materials and subject, but it’s this tension that makes the work so captivating, so alive.

The great tragedy is that Eardley never lived to fulfil her potential and never found real peace, either personally or as an artist. We can only imagine what ground she would have covered in her restless quest for artistic perfection had she survived. But what we do know is that her legacy endures, not only as a hugely popular artist but as an influential and truly first-rate one.

It’s a shame that there’s no full-scale exhibition of Eardley’s work anywhere this year but visitors curious to see why, at her best, she might be ranked alongside Auerbach, Bacon, de Kooning or any other big (male) baboons of postwar expressionism will find ample evidence scattered through the many shows on offer from Aberdeen to Dumfries, and even Hampshire.