He devoted time to a number of civil and human rights organizations,[1] was one of the early leaders of the Chinese Benevolent Association in Vancouver, and was "perhaps the most influential person" in the city's Chinatown.

[5] Foon Sien sought to end discrimination against Chinese Canadians and other minority groups,[6] and was an ardent activist to grant or recognize their rights, particularly regarding immigration[5] and family reunification.

[2] Their hopes were dashed when revolutionary Sun Yat-sen visited Cumberland from his exile in the United States on a fund-raising trip in 1911, leaving an impression on Foon Sien, who resolved to study law.

He founded the Kwong Lee Tai Company, a Chinese legal brokerage that employed interpreters to handle a wide range of cases, including civil and criminal matters such as immigration, deportation, merchant certificates, contracts, and leases with Westerners.

[18] In 1944, he drafted and signed a petition with Gordon Won Cumyow, Esther Fung, Ann Chian, Joe Leong, Henry Lee, and Andrew Lam as members of the Chinese Canadian Association.

[2] Despite this, Foon Sien was viewed as a controversial figure by some in the Chinese community, who believed he was "manipulating the CBA for his personal aggrandizement",[17] or resented him being referred to as "mayor of Chinatown" by the mainstream media, though such criticism was not widespread.

[28] The RCMP conducted raids of residences, businesses, and organizations of leaders of Chinese Canadian communities, seizing passports, visas, and other documents.

[28] Foon Sien considered these raids to be part of systemic human rights violations: "The situation resembles a country under martial law.

He believed that the project would create a barrier, likened to "the equivalent of a Berlin wall," separating the business and residential areas of Chinatown.

[3] It would raze 30 acres for a high-rise building at MacLean Park and the Raymur-Campbell public housing project,[30] some of which was land expropriated from Chinese property owners.

[3] However, Vancouver City Council approved the developers plans the subsequent week, but also stated they'd accept input from architects consulting for the CBA.