Dance Monkey, the song that changed Toni Watson’s life, was the byproduct of an unhappy episode while she was busking in Byron Bay, New South Wales. Heckled by a group of drunks, she wrote a deceptively buoyant synth-pop track about it. Driven by her divisive voice – childlike in timbre, but powerful – it reached No 1 in 30 countries. Tonight – “the biggest show I’ve ever done,” she marvels – she alters the backstory, saying she wrote it “to make people want to dance”. Watson and the song can be taken either way: as a one-woman celebration of getting your party on, or as a retort to bullies who “savagely” (her word) criticise her voice and appearance, an ongoing problem.

Unprepared for this level of success, she’s facing a full venue with a keyboard, a modest lighting rig and a dozen songs, mainly from her street-singing days. But for a performer seasoned by playing to derisory Australians, a roomful of effusive Londoners is easy. When she arrives, shielded by layers of sportswear and the omnipresent baseball cap, she’s already dancing. Sparse openers Can’t Be Happy All the Time and Never Seen the Rain set the no-frills tone, and she powers through the set by force of personality and that extraordinary voice.

There are anecdotes to go with most of the tunes: being underestimated by a California producer generated You’re So Fucking Cool; a friend coming out to his family inspired Johnny Run Away. It’s a rudimentary show, executed under the murkiest possible purple lighting, and not every song sticks, but Dance Monkey makes a warming and moving penultimate number. Like Watson herself, it offers bravery and charm in equal measure.

• At Vicar Street, Dublin, 3 March, and SWG3, Glasgow, 4 March.