Kasatkina has been playing on the tour as a neutral athlete after Russian and Belarusian players were banned from competing under their own flags following Moscow's invasion of Ukraine in 2022.
Kasatkina, who has not returned to Russia in more than two years after coming out as gay and being one of the few Russian players who has publicly spoken out against the war, lives in Dubai.
"Australia is a place I love, is incredibly welcoming and a place where I feel totally at home," she wrote in a message posted on Instagram. "I love being in Melbourne and look forward to making my home there."
She added that she would begin representing her new homeland immediately.
"Obviously, there are parts of this decision that have not been easy," she then wrote before thanking her family, coaches and supporters.
"I will always have respect and fond appreciation for my roots, but I am thrilled to start this new chapter in my career and my life under the Australian flag."
The 27-year-old has been as high as world number eight and has eight WTA titles to her name, with her best Grand Slam result coming when she made the French Open semi-finals in 2022.