Under Tarzan (1998–2013) Rivera began his career in public service in 1998, serving as a Community Affairs Officer under then-Mayor
Carmelo “Tarzan” Lazatin. He later held positions as Executive Assistant III and Officer-in-Charge of the Local Urban Poor Affairs and Housing Office (LUPAHO) until 2007.
LUPAHO Issue Rivera conducted a ceremonial turnover of land titles to TB Pavilion residents in 2020, despite no longer being affiliated with the Local Urban Poor Affairs and Housing Office (LUPAHO). His brother, Atty. Willie Rivera, then City Administrator, claimed Amos had no authority to distribute the titles and accused him of misrepresenting his role. The City Government questioned why the
Registry of Deeds released titles to Amos instead of LUPAHO, suggesting possible procedural violations.
City Councilor (2013–2022) Rivera was elected City Councilor of Angeles City and later served as Chairman of the Committee on Urban Poor Affairs. During his tenure, he passed ordinances such as a local Solo Parents Act and land title facilitation projects. He purportedly helped over 20,000 informal settler families obtain land titles and wellness benefits. == Mayoral and Vice Mayoral campaign ==