Chua said he was taking a "new journey, a journey of change".
"I'm convinced that today I'm standing on the right side of history, especially at this defining moment of history, I'm joining this party," he told a crowd of some 800.
He was with PKR de facto leader Anwar Ibrahim at the PKR's 'The Truth Behind the Scandals: Perak, PKFZ and the BN Conspiracy' forum in Sunway Resort Hotel & Spa.Chua said he decided to join PKR because the country's two-coalition political system was being undermined by Umno.
The death of Teoh Beng Hock, the political aide of Selangor executive councillor Ean Yong Hian Wah, was the “tipping point” in his decision to defect to the opposition, he added.
On Thursday, Teoh's body was found sprawled on the roof of an adjacent building after he had undergone questioning late into the night at the offices of the Malaysian Anti-Corruption Commission (MACC).