After Xavier Becerra resigned as attorney general to become Secretary of Health and Human Services, Bonta was appointed by Governor Gavin Newsom to replace him.

The Bonta family initially lived in a trailer at Nuestra Señora Reina de la Paz, the United Farm Workers headquarters near Keene, California, before moving north to Fair Oaks, a suburb of Sacramento.

[9] After his year at Oxford, Bonta returned to New Haven to attend Yale Law School while concurrently working as site coordinator at nonprofit organization Leadership, Education, and Athletics in Partnership (LEAP), where he developed policy and managed activities for 30 staff members and 100 children for an organization serving the Church Street South neighborhood.

Working at Keker & Van Nest from 1999 to 2003, Bonta practiced in a variety of areas including civil rights, crime, insurance, patent infringement, legal malpractice, contract, and fraud.

[7] As a private attorney, Bonta was part of a team that worked with the ACLU to implement new protocols to prevent racial profiling by the California Highway Patrol.

In 2012, some Alameda residents started a recall campaign against him but the effort never qualified for the ballot, with Bonta winning election to the state assembly in November 2012.

In February 2021, CalMatters reported that Bonta had regularly solicited donations, also known as "behested payments", from companies with business before California's legislature for his wife's nonprofit organization.

[16] As a member of the state assembly, Bonta authored major changes to California's penal code, as well as immigration, health care, and housing law.

[20] Bonta introduced legislation in January 2013 that would require California public schools, as funding is available, to teach students "the role of immigrants, including Filipino Americans" in the farm labor movement.

Signed in 2019 by Gavin Newsom, AB 32 made California the first state in the nation to ban both private prisons and civil detention centers.

[31] On March 24, 2021, Governor Gavin Newsom announced that he would be appointing Bonta as Attorney General of California to succeed Xavier Becerra, who had resigned the position to become Secretary of Health and Human Services under President Joe Biden.

[39] In January 2023, Bonta and attorneys general from seven other states joined the Department of Justice in filing an antitrust lawsuit against Google's advertising technology (adtech) market practices.

[41] In response, Bonta noted that "SB9 does not allow for entire towns or cities to be declared off limits" from the law, and that exceptions require "a parcel specific inquiry".

[44] Bonta condemned the incident, saying, it was "unacceptable and falls short of...expectations for this department", and that he was "deeply disturbed and angered", while his office said it was investigating how much information might have been exposed.

The breach exposed personal data that included names, dates of birth, gender and race, driver’s license number, addresses, and criminal history.

[45] The California Rifle & Pistol Association said the breach "put the lives of judges, prosecutors, domestic violence victims and everyday citizens at risk" and gave criminals "a map to their homes".

[53] Their daughter, Reina, is a filmmaker and plays soccer for the Brazilian club Santos FC, which competes in the Brasileirão Feminino, and the Philippines national team.