IF the mark of superstardom is being known by one’s first name only, Judy Garland got there long before Madonna and Beyonce. Will there be movies about them in half a century’s time?

Then again, to the Beyonce generation, Judy Garland is ancient history. Yet her life should be a timeless cautionary tale of fame won early and exploited ruthlessly, sometimes by the lady herself but mostly by others.

In this stirring biopic, Renée Zellweger channels Garland with uncanny exactness, but above all with love and sympathy. This is a billet-doux from Renée dearest to darling Judy, a nod to all that what went before and happens still.

Directed by Rupert Goold (The Hollow Crown, True Story), Judy takes as its central point Garland’s Talk of the Town concerts in London, 1969. By the time she arrived that December she had gone from famous to infamous, her dependence on booze and pills legendary, her no-shows frequent.

The impresario Bernard Delfont (played here by Michael Gambon) assigned an assistant, Rosalyn Wilder (Jessie Buckley), to keep Garland on track. Boy was she needed, as we see from one thrilling sequence when Garland, battered by nerves and already late for her show, has to be fetched from her hotel, dressed, made-up, and hurried on stage.

By way of explanation, the picture spools back and forth from London to her Hollywood beginnings. It is a familiar story, born in a trunk in the theatre, performing from age two, signed by MGM at 13, all that oft played jazz, but there is a sinister air hanging over this period. The yellow brick road, the film suggests, was Garland’s road to hell.

Yet that seems too simple and neat a conclusion, and one, moreover, that robs Garland of any personal responsibility. True, Zellweger does not portray her as some angel fallen to Earth. There are flashes of temper, of the diva, the plain old pain in the neck, that she could be. But because the story deals with the beginning and end of her career, with nothing about the middle, it feels like a story half told.

Buckley, last seen as a Glaswegian country music singer in Wild Rose, is outstanding, and the relationship between the two women is one of the film’s treasures.

But let’s face it, Judy stands or falls by the lady herself, Zellweger, and she is wonderful. This is not the role that got away. Tiny, as frail and sparrow-like as Piaf but with a voice that could punch a hole in a wall, she looks and sounds more like Garland than anyone I’ve ever seen. Though the impression occasionally feels too mannered, even that fits. What was Garland by the end but Judy playing Judy?