The 39-year-old, who played 44 international matches for Australia, including 24 T20Is, has completed the ICC's mandatory three-year stand-down period after his last appearance for Australia in 2021, making him eligible to switch allegiance.
Born in Funchal, Madeira, the birthplace of Cristiano Ronaldo, Henriques said the move is driven by both his Portuguese heritage and his desire to help cricket grow globally.
He added that his family in Portugal is proud to see him represent their country.
"I guess the opportunity for growth in the game around the world, it's probably not just my Portuguese heritage, but the game, more importantly, and the opportunity for growth worldwide. We can improve the quality of all the engagement in, say, another 10 or 20 nations around the world, and then you're looking at cricket World Cups that stop the entire world, as opposed to a couple of Western countries and the subcontinent," Moises Henriques said to the Australian outlet CODE Sports.
"My family back in Portugal would be all really proud to see me doing it as well. Both my brothers think it's cool, they were both born here in Australia after we moved here, where I was actually born in Portugal. My family that are still in Portugal, they seem more proud than anyone, so yeah, even though I haven't really been a huge part of their lives, but I think they see it as 'oh wow, we've got someone in the family that's representing our country, as opposed to another country'," he added.
Henriques, who remains active as captain of the Sydney Sixers in the Big Bash League, is set to follow former Australia batter Joe Burns, who switched to represent Italy in international cricket.