The 28-year-old had been in Chinese custody for more than two weeks. He had been accused of violating public security management regulations while in the city of Shenzhen, just across the bay from Hong Kong.
British consulate employee Simon Cheng Man-Kit was released on Saturday morning, after 15 days in administrative detention in China, according to Shenzhen police.
Authorities issued a short statement on social media, saying Cheng had been set free as scheduled and his rights had been protected "in accordance with the law."
The Hong Kong resident was detained after visiting the neighboring city of Shenzhen, which is in mainland China, on August 8.
Cheng was detained for more than two weeks for breaking a public security law.
Police in Shenzhen's Luohu district said he had "confessed to his illegal acts," without giving specific details.
"Simon has returned to Hong Kong," his family said on Facebook, adding that he would take "some time to rest and recover."
His release was also confirmed by Max Chung, who had been lobbying the UK government to step up efforts to free the consulate staffer.
Meanwhile, Hong Kong has been bracing for more protests as the pro-democracy movement marks its 11th weekend. In addition to rallies, the activists pledged to conduct a "stress test" of transport links leading to the city's airport, after a court banned new protests at the site.
Posters circulating online urged the protesters to "drag" their feet and be as slow as possible, aiming to cause disruption. Roads and railways leading to the airport operated normally as of Saturday morning.
Elsewhere, however, the city's MRT rail company closed four subway stations near the Kwun Tong area, where one of Saturday's rallies was due to be held. On Friday, the transport company said that it had been given an injunction to prevent protesters from disrupting services, and that it could immediately stop operating if "fights, vandalism or other acts of violence occur" at its stations.
Previously, Chinese state media criticized MRT for allowing "rioters" to leave the scene by train after clashing with police.
jsi,dj/rc (dpa, Reuters, AP, AFP)