Dong Jingwei has been appointed head of China's national security office in Hong Kong, the country's ministry of human resources said in a statement on Tuesday.
Dong was previously China's top spy catcher who had oversight of counter-intelligence. He was also vice-minister of state security, a high-profile role which included hunting down foreign spies in China and nationals who colluded with foreign countries.
Originally from China's northern Hebei province, Dong has decades of experience working through the country's security apparatus.
Hong Kong's office for safeguarding national security was set up in 2020 following Beijing's imposition of a national security law in the Chinese-controlled territory that year.
Western governments including Britain and the US have criticised the law as being a tool to crush dissent.
Chinese and Hong Kong authorities say the law, which punishes subversion, collusion with foreign forces and terrorism with up to life in prison, has brought stability after the 2019 protests.