The royal couple arrived in Sydney on a Royal Australian Air Force plane on Friday evening, and were greeted on the tarmac by Prime Minister Anthony Albanese, Australia's Governor-General Sam Mostyn and the premier of New South Wales state Chris Minns.
King Charles carried an umbrella and chatted with the welcoming party, as rain cleared for the royals' arrival.
The couple travelled in a motorcade to Admiralty House, a historic government foreshore residence overlooking Sydney Harbour and the opera house, where they will meet privately with Albanese and his partner Jodie Haydon.
Sydney's Opera House displayed a photographic montage of King Charles's previous visits to Australia, where he attended school for six months as a teenager, and has returned more than a dozen times.
King Charles is making his inaugural visit to an overseas realm as sovereign, his first major foreign trip since being diagnosed with cancer.
Earlier, the royal couple wrote on social media platform X, "We are really looking forward to returning to this beautiful country to celebrate the extraordinarily rich cultures and communities that make it so special."
The couple are visiting Sydney and Canberra over six days, before travelling to the Commonwealth Heads of Government Meeting in Samoa.
The official programme begins on Sunday in Sydney.
(Reporting by Kirsty Needham in Sydney; Editing by Jan Harvey and Kim Coghill)

King Charles III and Queen Camilla arrive at Sydney Airport on October 18, 2024 in Sydney, Australia. The King's visit to Australia will be his first as Monarch, and CHOGM in Samoa will be his first as Head of the Commonwealth. (Photo by Brook Mitchell/Getty Images)