First term, 2020–2024
In 2019, Hung sought the Kuomintang nomination for the New Taipei City first constituency and defeated former legislator Wu Yu-sheng in the party primary. The constituency comprises the districts of Tamsui, Bali, Linkou, Taishan, Sanzhi, and Shimen. In the January 2020 legislative election, Hung received 119,401 votes and defeated incumbent Democratic Progressive Party legislator Lu Sun-ling, who received 110,162 votes. He took office as a member of the 10th Legislative Yuan on February 1, 2020.
Hung served on the Legislative Yuan's Transportation Committee during all eight sessions of the 10th Legislative Yuan. He was elected a convener of the Transportation Committee during its fifth session and also served on the Discipline Committee during that session. In March 2022, while serving as Transportation Committee convener, Hung scheduled a committee hearing at which the National Communications Commission was asked to report on controversies surrounding the licensing and management of Mirror News. During his first term he also served as a deputy secretary of the Kuomintang caucus in the Legislative Yuan.
On August 30, 2022, the Kuomintang appointed Hung chairman of its Culture and Communications Committee, succeeding Wang Yu-min, who had entered the 2022 local election campaign in Chiayi County. Hung stepped down as Culture and Communications Committee chairman on May 3, 2023, after the Kuomintang nominated him to seek reelection in New Taipei City's first constituency. He remained a member of the Kuomintang Central Standing Committee after leaving the communications post.
Second term, 2024–present
Hung was re-elected to the Legislative Yuan in the January 2024 election with 158,596 votes, or 58.71 percent of the vote. His 158,596 votes were the largest raw vote total received by any elected legislator in the 2024 election. He began his second term as a member of the 11th Legislative Yuan on February 1, 2024.
Shortly before the new legislature convened, the Kuomintang caucus selected Hung as its secretary-general for the first session of the 11th Legislative Yuan, alongside caucus whip Fu Kun-chi and chief deputy secretary-general Lin Szu-ming. Hung served on the Education and Culture Committee during the first and second sessions of the 11th Legislative Yuan and also sat on the Procedure Committee during the first session. He left the caucus secretary-general position before the second session, when Lin Szu-ming succeeded him in the post.
Beginning with the third session, Hung returned to the Transportation Committee. He served as one of the committee's conveners during the fourth session and remained a Transportation Committee member during the fifth session in 2026.
In 2025, voters in Hung's constituency initiated a recall effort against him. The recall petition's stated grounds included criticism of legislation Hung had proposed or co-sponsored, his role in reductions to government budget items, his positions on cross-strait and national-security issues, and his conduct as a legislator; Hung rejected the allegations in his formal response and defended his legislative and constituency record. The recall vote was held on July 26, 2025. The proposal was defeated, with 94,808 votes in favor of recalling Hung and 121,592 votes against, while the number of votes in favor also fell below the statutory threshold of one-quarter of eligible voters.
