The photo shows Trunfio staring directly into the camera as she feeds her daughter.
"Shout out to #women all over the world raising the next generation," she wrote.
Her post caught the attention of fellow women and mums, who thanked the model for sharing the "real" selfie.
"I love seeing you share content like this; you're such an inspiration," one follower said.
"So beautiful mumma! The female body is a miraculous thing," said another, while others shared similar joys.
"Isn't it amazing and such a beautiful thing. I miss these moments so much," a woman wrote.
"I always felt like a superhero the nine months I was breastfeeding."
The 34-year-old model has always been a big advocate in normalising breastfeeding.
In 2015, Trunfio graced the cover of Elle Australia breastfeeding her son Zion, in a timeless image captured by photographer Georges Antoni.
It was part of a larger campaign to raise awareness about breastfeeding and dispel taboos around it.
"When I saw the cover of me breastfeeding, which was unplanned and just natural, I teared up and thought, 'Wow this is such a special moment where my worlds have collided'," Trunfio said at the time.
"There is nothing more powerful and beautiful than motherhood. The last thing I want to do is be controversial, so please take this for what it is, let us #normalisebreastfeeding there is nothing worse than a mother that is judged for feeding her hungry child in public."
Trunfio went on to say she "obviously" doesn't "look like this or wear (this)" while breastfeeding but explained it stands for all women out there.
"Whether you breastfeed or not, we gave birth, we are women, we are mothers."
The photo also marked the first time an Australian magazine published a cover shot of a mother nursing her child.
"There should be NO JUDGEMENT of a mother doing what is a god-given gift, feeding your baby or in some cases another woman's baby," Trunfio said in a reflection post in August last year.
