[2] He was a member of the Legislative Assembly (MLA) of British Columbia, representing the electoral district of Matsqui from 1994 to 2001, Abbotsford-Mount Lehman from 2001 to 2009, and Abbotsford West from 2009 until 2024.

De Jong was born to Dutch parents who immigrated to Canada after Canadian soldiers liberated the Netherlands in World War II.

[6] He was regarded as very vocal on the opposition benches; he was ejected from the legislative assembly for calling then-Attorney General Colin Gabelmann a "liar" and was later sued for libel by federal cabinet minister Herb Dhaliwal.

[8][14] On two occasions in 2010, de Jong stepped in as Minister of Public Safety and Solicitor General while Kash Heed was under investigation for campaign violations.

[8][15] That same year, de Jong faced controversy when he approved the payment of $6 million in legal fees for Liberal Party insiders David Basi and Robert Virk, who pleaded guilty to charges of breach of trust and accepting benefits in connection with the sale of BC Rail in 2003.

[16] On December 1, 2010, de Jong announced that he would seek the leadership of the BC Liberal Party to replace the outgoing Gordon Campbell, and resigned his cabinet post.

[27] With Christy Clark resigning as leader, de Jong announced on September 26, 2017 his intention to run in the 2018 BC Liberal leadership election.

[29] On January 18, 2018, de Jong and rival candidate Andrew Wilkinson announced they had struck a deal to support each other as their second-ballot choices.

[35] On March 4, 2025, de Jong revealed on social media that despite the local Electoral District Candidate Selection Committee unanimously endorsed his candidacy, the party denied his application to seek the nomination.