Former union leader Carol Ng Man-yee, and activists Nathan Lau Chak-fung and Frankie Fung Tak-chun were the third batch of defendants in the landmark case to complete their four-year-and-five-month sentences.
The trio, who pleaded guilty, were separately sent to their residences in vans from the Lo Wu Correctional Institution and Stanley Prison on Monday morning.
Asked about his feelings, Lau put on a smile and shook his head while walking towards his block.
Lau, 28, was the president of the student union at Hong Kong Shue Yan University and a standing committee member of the Hong Kong Federation of Students.
Ng, now 54, was a flight attendant at British Airways. She founded the BA Hong Kong International Cabin Crew Association and had mounted several legal challenges against the employer over wages, anti-union practices, age and sex discrimination.