Former lawmaker Lam Cheuk-ting from the Democratic Party was arrested on Monday morning and charged with revealing the identity of a person under investigation by the ICAC.
A video uploaded to Lam's Facebook page showed three ICAC officers arresting him at his home.
Lam opened the gate after conversing with the officers, telling them that he was only being arrested for political reasons.
"Arresting me today clearly marks the fall of the ICAC," Lam said. "It again demonstrates the fall of Hong Kong."
The person under investigation was said to be linked to the Yuen Long mob attack that took place on July 21 last year.
"Lam Cheuk-ting, 43, faces three counts of disclosing identity of persons being investigated, contrary to Section 30(1)(b) of the Prevention of Bribery Ordinance (POBO)," the ICAC said in a statement.
Lam, a former investigator with the anti-graft body, later appeared before Eastern Magistracy wearing a T-shirt bearing the ICAC logo.
The case was adjourned until early March and Lam was released on bail of HK$2,000.
The ex-lawmaker had earlier been charged with rioting over the Yuen Long attack.
He was among dozens of people injured when more than 100 men armed with bamboo sticks and clad in white T-shirts attacked people indiscriminately at Yuen Long MTR Station.
Lam is due to appear in the District Court on January 5 over the rioting charge.
Last updated: 2020-12-28 HKT 15:30