An unknown Melbourne artist, Lynn Savery, said she “really thought she was going to faint” after winning the $150,000 Doug Moran national portrait prize, for a self-portrait which she says aims to challenge “socially constructed” gender norms.

The 58-year-old artist from East Kew has been a full-time carer until recently, and was unknown before Thursday morning’s announcement; she has no artist website, and has not been accepted into a painting prize before. This is her first oil painting and her first portrait, but she has “dabbled in drawing and other things,” she told Guardian Australia.

Savery has a background in furniture design, and a PhD in international politics and human rights. Most recently, though, she’s been looking after her husband, who has cancer, and her father, who had dementia until he died in February this year, on her birthday.

Her husband is at home, looking after their blind shih-tzu. “He has made it through so far, but it’s been a gruelling time … it leaves you kind of shattered,” she said. “Painting was really just about being able to have a bit of peace and quiet … it was a respite, I suppose.”

In her artist statement, Savery said she posed with a manspread and “casual lean” to “illustrate how body posture contributes to gender stereotypical impressions”. She told the Guardian: “That’s the feminist in me! Did you know they banned manspreading in Madrid? I was like, ‘Yay!’”

Savery said she was happy with how she comes across in the work. “I wanted to see how I saw myself, how it reflected back as I painted. I suffered from terrible depression 10 years ago, and get terrible anxiety now as a result, but I also love life. I wanted to see what shows through – and I was pleased to see it was not a dark painting.”

At her feet in the portrait sits an English bulldog, Clementine: “[She] is a good friend of mine and I wanted to capture her physical and emotional presence in this work.”

Due to the nature of the prize, which is to be kept unknown from the winner until the announcement, the publicist said she was unable to ascertain anything about the winner other than the suburb she lived in, and – thanks to a thorough online search – her proclivity for vintage clothes.

Savery almost fainted when she was announced the winner. “My knees were turning to jelly and I thought, oh jeez, I’m going to cry. And I did – well, I sort of managed to just hold it off, but I kind of just wanted to run away!”

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Her work was selected over paintings by Doug Moran and Archibald prize luminaries such as Vincent Fantauzzo, who painted Asher Keddie; Nick Stathopoulos, who painted fellow artist Natasha Walsh; and Peter Smeeth, who painted Kate McClymont. Past winners include Prudence Flint, Ben Quilty, Tim Storrier and Fiona Lowry.

The surprise win has resonances with Warren Crossett’s win of the 2015 prize for his own self-portrait – the first prize he had ever entered. (“My wife is going to lose the plot when she finds out,” he told Fairfax at the time.)

The Doug Moran winner was drawn from a shortlist of 30 finalists, who each receive $1000, and who were selected by the three judges: artist Louise Hearman, who won the 2014 Doug Moran and 2016 Archibald prize; art historian and former director of the National Gallery of Australia, Dr Ron Radford; and Greta Moran, who established the Moran Arts Foundation with her husband Doug in 1988.

“We admired the meticulous attention to detail and beautiful placement of the figure and her dog,” said Ron Radford of Lavery’s winning portrait, which was chosen unanimously. “The portrait had a real impact in its direct gaze to the viewer as only a good self-portrait can achieve. Her colouration was finally calculated, overall, a very engaging portrait.”

Facebook Twitter Pinterest Lynn Savery with her Doug Moran prize-winning self-portrait. Photograph: Carly Earl/The Guardian

Hearman said the prize money can be a “massive” life change. “You’re able to proceed with things you were planning to do without having to worry ... Australian artists, very few do make enough money to only paint, and not have another job. So it gives the winners a chance to just paint solidly for a few years.”

Awarding the prize, Hearman praised Savery’s “obsessive eye for detail” and ability “to make the entire painting sing as a whole. It has emotion, beauty and love of life’s visual stories. The painting is full of invention, sophisticated colour and defiant SPLAT in your face appeal”.

To the Guardian she elaborated, “If you look at that fine detail – even just the zipper, the nice yellow lines – she’s really obsessed with detail ... that’s what keeps drawing you back in.”

Hearman said the winner distinguished itself from some other entries which “were initially very interesting in a photograph, but when I saw them in person, they were actually photographs. As in, they started as a photographed image and then got painted over, and became a painting. Which, I’m not sure about the rules of the prize, but in actual fact those pictures weren’t as interesting in person – and so naturally they didn’t make it in [to the finalists]. I don’t know, maybe they need a ‘paintograph’ section of the prize. It’s an interesting grey area.”

Celebrating its 30th year, the Doug Moran is the world’s richest portrait prize, asking artists to “interpret the look and personality of a chosen sitter, either unknown or well-known”, differentiating itself from the Archibald prize, which asks for portraits of a “man or woman distinguished in art, letters, science or politics”.