Cavallo, who plays for A-League side Adelaide United and has represented Australia at Under-20 level, becomes the only current top-flight male professional footballer in the world to reveal he is gay.
He announced the news ahead of the new A-League season in a lengthy social media post.
The 21-year-old said it was 'astonishing to know there are no gay professional footballers who are out and actively playing' and that he wanted to show 'others who identify as LGBTQ+ that they are welcome in the football community'.
In his post, Cavallo said: "Being a gay closeted footballer, I've had to learn to mask my feelings in order to fit the mould of a professional footballer.
"Growing up being gay and playing football were just two worlds that hadn't crossed paths before.
"In football, you only have a small window to achieve greatness, and coming out publicly may have a negative impact on a career.
"As a gay footballer, I know there are other players living in silence.
"I want to help change this, to show that everyone is welcome in the game of football, and deserves the right to be their authentic self."
Cavallo has been widely praised for his announcement, with Chelsea women's star Sam Kerr tweeting 'Good for you' with a love heart emoji, while Arsenal's Caitlin Foord added: "Respect, the strength to speak out and own who you are."
Arsenal Football Club as a whole sent a touching message to Cavallo, too.
Quote tweeting Cavallo's social media statement, the Premier League side said: "Thank you @JoshuaCavallo for your strength and bravery…
"You are an inspiration to millions. Everyone deserves the right to be themselves. The world of football is a better place today, because of you."
Meanwhile, Barcelona defender Pique reached out to Cavallo, crediting the 21-year-old with helping move the game forward.
Quote tweeting Cavallo's social media statement, Pique said: "Hey @JoshuaCavallo, I don't have the pleasure to [sic] know you personally but I want to thank you for this step that you take [sic].
"The world of football is far behind and you are helping us move forward."
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