Sydney artist Tony Costa had been studying law for more than two years when he went to his mother, standing at the kitchen sink of the family home in Strathfield, undecided if he should continue with law.

"I said, 'What do you think I should do? I'm torn.' And without turning she said, 'Follow your heart.' But I thought she said, 'Follow your art.' "

Costa's heart had resided in painting since the age of 13 and that decision to quit legal studies and enrol at Julian Ashton Art School took him on Friday to the Art Gallery of NSW, where he was named winner of Australia's most recognisable portrait prize for a meditative portrait of artist Lindy Lee.

"It was the best advice I was ever given," he said, paying tribute to his late mother who did not live to see the win, a moment Costa described as nothing less than a "miracle".