In 1985, at the age of 15, Chia was sentenced to two years' probation by a juvenile court following an incident where he and group of other boys broke into a school and committed vandalism. In his book Called to Serve, Chia notes that the incident left him determined to turn his life around. He went on to graduate from Nanyang Junior College in 1988.
During his national service, Chia became an officer in the Singapore Armed Forces despite the discovery of an inborn heart defect late in his officer cadet training which resulted in him being put on light duties for the final two months of the course. His commanders were nevertheless impressed by his performance and wrote in to appeal for him to be commissioned as an officer. The appeal was approved, and he became the only person to have graduated from the Officer Cadet Course without taking the senior term Individual Physical Proficiency Test (IPPT) and Standard Obstacle Course.
Chia then became a student at the National University of Singapore (NUS), where he read Psychology and Philosophy. He graduated with a Bachelor of Arts degree in 1994. He was active in student politics during his time at NUS, and was elected the President of the National University of Singapore Students' Union (NUSSU) in 1993.
Chia first took an interest in national politics during a by-election in the Marine Parade Group Representation Constituency in 1992, when he attended one of the National Solidarity Party's campaign rallies. (He had intended to attend a rally of the Singapore Democratic Party, for whom Chia's Psychology lecturer Chee Soon Juan was standing as a candidate, but he went to the wrong location and ended up at the NSP's rally instead.)
After graduating from NUS in 1995, Chia joined the NSP. At the 1997 general election, he was a member of the party's teams in the Hong Kah Group Representation Constituency, and was defeated by the team from the governing People's Action Party (PAP) by 36,920 votes (31%) to 82,182 (69%).
Prior to the 2001 general election, the National Solidarity Party joined the Singapore Democratic Alliance.
Chia stood as the SDA's candidate in the single-member constituency of Chua Chu Kang at the 2001 general election. During the election campaign, Prime Minister Goh Chok Tong unexpectedly praised Chia, noting that he appeared to be more professional than many of the other opposition candidates. (Goh later claimed that he did so because he was confident that the PAP candidate in Chua Chu Kang would win, but wanted to help Chia claim and a Non-constituency MP's seat. In his book Called to Serve, Chia speculates that Goh did this because he remembered Chia from discussions they had had in 1993 about the establishment of the NUS Students' Trust Fund.) Chia was defeated by the PAP's Low Seow Chay by 8,143 votes (34.66%) to 14,489 (65.34%). As this was the highest percentage of the vote garnered by any opposition losing candidate at the election, Chia therefore became a Non-constituency MP.
At the 2006 general election, Chia improved his percentage of the vote in Chua Chu Kang, but still lost to the PAP's Gan Kim Yong by 9,292 votes (39.63%) to 14,156 (60.37%). This was not enough to enable him to hold on to his NCMP seat as the team from the Workers' Party in the Aljunied Group Representation Constituency won 43.91% of the votes. (The Workers' Party's Sylvia Lim became the next NCMP.)
Chia contested a fourth time in the 2011 general election in the newly carved out single-member constituency of Pioneer against the PAP's Cedric Foo, who was already the MP for the district when it was part of the West Coast Group Representation Constituency. However Chia fell short again, winning 39.27% of the votes.
Ahead of the 2015 general election, the NSP announced that it planned field Chia as a candidate in the single-member constituency of MacPherson. This was a controversial decision as the Workers' Party had already announced that it planned to field a candidate against the PAP in the constituency. The NSP's Acting Secretary-General, Hazel Poa, resigned from the party following the announcement stating that she disagreed with the decision of the party's Central Executive Committee to contest the constituency. On 22 August 2015, Chia released a statement on Facebook announcing that he had decided not to be the NSP's candidate in MacPherson and would not be standing in the general election. He stated that "the Trolls have won" because negative online posts had been a key factor in his decision to withdraw. (The NSP subsequently decided to field Cheo Chai Chen in MacPherson.)
In 2003, while Chia was an NCMP, he was involved in a scandal when topless photos of a maid who worked in his home were discovered by his wife in his computer's "recycle bin". His wife lodged a police report. Chia insisted that his maid had agreed to pose for the photos and that he did not force her to do so. He noted that he had an interest in nude photography, and even showed the press nude photos that he had taken of himself (with his back to the camera) to prove this. Police investigations found no evidence that an offence had been committed.
In 2006, Chia was fined following an incident when he drove a car through a red light, causing a crash with a bus.