The work, showing Dalman barefoot and seated, her long silver hair flowing down, has an unfinished quality; her face is detailed, while her hands and feet are mere sketches.

But it was this very quality that beguiled the judges, who anointed da Silva the winner of the inaugural $75,000 Darling Portrait Prize at the National Portrait Gallery on Thursday.

Da Silva was one of the 40 finalists, only half of whom are established artists, whose works are now showing at the gallery, selected from a pool of 331 entries.

Gallery director Karen Quinlan, head of the ANU School of Art and Design Denise Ferris, and director of the National Gallery of Victoria Tony Ellwood said the portrait of Dalman had succeeded in revealing "the fragile, fluid nature of the human body".

"Here is a woman who has spent her life moving, and while she is captured here sitting, she looks set to leap," they said. "We were struck by the deliberate power of the seemingly unfinished elements of the work because, like Elizabeth, the complete picture is yet to be filled in - there is much yet for her to do."

Da Silva, based in Griffith, NSW, said she had tried for some time to capture Dalman on the canvas, using different styles, but eventually realised that the subject herself was "a continuous series of sketches".

She said leaving the work seemingly "unfinished" had been a gamble.

"I overdid it - there's bits there I could probably go over and change a little bit of today, so it's about stepping away," she said. "I've taught tertiary-level and regular drawing classes, and when you know you're having that smitten-ness with something that's happened, that's a really good time to just step away from the canvas."

Judge Denise Ferris said the judges had been unanimous in both selecting the finalists and deciding on a winner.

"What's so wonderful about this winning portrait is that it's very alive, it's very dynamic...it's got an untidiness about it," she said. "It's one of those works where it might be easy to see its unfinished qualities, when in fact what the painter has, I think very courageously, done, is know where to stop."

Dalman herself, seeing the portrait up close for the first time, said she was struck by its "lightness". Living at Lake George and described by many as the 'high priestess' of Australian contemporary dance, Dalman has been photographed countless times, but said she was often critical of how pictures of herself turned out.

"But I actually like this very much," she said. "My recent work is called Crone, so I'm really proud to be a longer-living woman, and I think we need to share our experiences about that. In our society, the older woman is often invisible or put aside and not listened to ... So personally it's an extraordinary experience, but I think also for longer-living women, it's a wonderful thing and I feel thrilled about that."