[4] Tsai was first elected to the Legislative Yuan in 1998, taking office as a political independent representing Pingtung County.

[5] In May 2000, Tsai co-initiated a signature drive within the Legislative Yuan in support of the National Coalition Government of the Union of Burma.

[6] He was the convener of the National Non-Party League,[7] and helped reform a caucus for independents, known as the Non-partisan Alliance, during his next term in 2002.

[8][9] Tsai was one of ten founding members of the Non-Partisan Solidarity Union, established in June 2004,[10] and served the new political party as its legislative whip.

[12] In 2008, The Taiwan Tongzhi Hotline Association advised gay and lesbian voters not to vote for a list of political candidates, including Tsai, that the organization considered to be opponents of LGBT rights.

[15] During a January 2007 budget vote and consideration of nominations to the Central Election Commission, Tsai joined Kuomintang colleagues rushing to legislative speaker Wang Jin-pyng as Democratic Progressive Party legislators sought to stall the vote by gathering at the speaker's podium.

"[20] Tsai sought election to the Pingtung County Council in 2009, and served as founding vice chairman of the Congress Party Alliance in 2018.

[26] In February 2009, Tsai was called as a witness for a hearing in which the Taipei District Court decided to grant Gary Wang bail.

[33] In a case of fraud dating to 2011, the Kaohsiung branch of the Taiwan High Court heard an appeal and convicted Tsai on charges of forgery in January 2021, sentencing him to four years and ten months imprisonment.

[38] The pair's election to the county council in 2009 marked the first time a married couple had served together on that legislative body.