[4] After graduating from the University of California, Irvine, he became an organizer for UNITE HERE Local 11 and involved with the Los Angeles chapter of the Democratic Socialists of America.

[7][8] In 2020, he was designated by his union to be the labor liaison on Measure J, a ballot initiative to allocate at least 10% of Los Angeles County's funding for community reinvestment and incarceration alternatives.

[21] As the only renter on City Council, Soto-Martinez pushed to expand tenant protections ahead of the expiration of Los Angeles' eviction moratorium that was instituted during the COVID-19 pandemic.

[29] In February 2023, Soto-Martinez introduced a motion with Councilmember Tim McOsker to reform the LAPD disciplinary system by making it easier to suspend or fire officers accused of severe misconduct.

[36] Despite previously expressed concerns, no major issues at the park were reported in the following months, leading to praise from community members, City Council colleagues, and Mayor Karen Bass.

[37][38] In March 2023, Soto-Martinez introduced a motion with Councilmembers Eunisses Hernandez and Nithya Raman to make Los Angeles a sanctuary city.

The motion would codify existing policies, including a 2017 executive directive issued by then-Mayor Eric Garcetti that prohibits all city employees from using public facilities or resources to assist or cooperate with federal civil immigration enforcement.

[40] In August 2023, Soto-Martinez along with Nithya Raman and Eunisses Hernandez voted against a four-year package of raises and bonuses for rank-and-file police officers.

[43][44][45] In June 2024, Soto-Martinez helped remove U-Turn signs that were considered discriminatory as they had been installed in the neighborhoods in 1997 to deter gay men from cruising the streets.