Returning to the area of her upbringing, in April 2014, Solis formally announced a campaign for a seat on the non-partisan Los Angeles County Board of Supervisors.

[3][4] Her father was a Teamsters shop steward in Mexico[5] and, after coming to the United States, worked at the Quemetco battery recycling plant in the City of Industry in the San Gabriel Valley.

"[7] She graduated from La Puente High School,[12] where she saw a lack of support for those wishing to continue their education,[6] including a guidance counselor who told her mother that "Your daughter is not college material.

[2] Solis served near the end of the Carter Administration in the White House Office of Hispanic Affairs,[2] where she was editor-in-chief of a newsletter during a 1980–1981 Washington semester internship[3][7][15] as part of her master's program.

[3] During her time on the board, she worked towards improved vocational job training at the college and sought to increase the number of tenured faculty positions held by minorities and women.

[3][6] When Governor Pete Wilson vetoed it, she organized a successful drive to make the issue into a ballot initiative the next year, using $50,000 of her own campaign funds and rallying union support.

[11] Solis held high-profile hearings on labor law enforcement following a summer 1995 sweatshop raid in El Monte that discovered more than 70 Thai workers existing in slave-like conditions.

"[11] Solis was an environmental activist in the State Senate, due to concerns that stemmed from a childhood spent within smelling distance of the Puente Hills Landfill[11] and making frequent visits to the San Gabriel Mountains.

[29] Calling for "the fair treatment of people of all races, cultures, and incomes with respect to the development, adoption, implementation, and enforcement of environmental laws",[30] it represented the first legislation of its kind in the nation and is considered a landmark.

[31] Due to her work in overcoming obstacles for environmental justice, in 2000 Solis was given the Profile in Courage Award by the John F. Kennedy Library Foundation, and was praised as "a politician who hasn't shied away from challenging the old boy network both within and without the Latino community".

[16] After months of deliberation, she decided to run for the U.S. House of Representatives in 2000 against 18-year incumbent Matthew G. Martínez in the 31st congressional district, which consisted largely of working class Hispanics and Asians.

[3] Solis was able to obtain the support of the Los Angeles County Federation of Labor (which called her a "warrior for working families"),[8] Emily's List, Handgun Control Incorporation, the Sierra Club and the California League of Conservation Voters.

[26] National Journal magazine named her one of its "Ten Freshmen to Watch", and said that her election "is a sign of things to come in California and a generational changing of the guard in the Hispanic Caucus".

[53] Solis believed in the importance of mentoring, and as a House member continued relationships she had established with up-and-coming political figures in her district, including California State Assemblywoman Judy Chu and Monterey Park Mayor Sharon Martinez.

[64] Committee chair Ted Kennedy repeatedly praised her, while, despite examination by Republican members, Solis declined to discuss specific policy issues, including the Employee Free Choice Act.

[8] In her first days as secretary, Solis affirmed an extension to unemployment benefits specified by the 2009 Obama stimulus package,[79] and joined Vice President Biden's Middle Class Task Force.

[80] In her first major speech as secretary, Solis pleased community forum attendees at Miami's Greater Bethel AME Church by vowing more aggressive enforcement of workplace protection laws, saying "You can rest assured that there is a new sheriff in town.

[95]) In February 2011, as protests continued over Wisconsin Governor Scott Walker's proposal to limit that state's public employee unions' collective bargaining rights, and similar proposals were made in other states, Solis spoke out strongly and emotionally against such moves, saying "[those governors] aren't just asking workers to tighten their belts, they're demanding they give up their uniquely American rights as workers.

[97] In October 2012, Solis defended the work of the Bureau of Labor Statistics, after the Current Population Survey it puts out monthly reported that unemployment in the United States had fallen below eight percent for this first time since Obama took office.

[98] Some critics, including former General Electric CEO Jack Welch, charged that the number had been tampered with in order to benefit Obama one month before the U.S. presidential election.

[102] Reflecting upon her tenure, Solis generally garnered praise from labor unions and leading Democrats for her stricter enforcement of job safety regulations and more aggressive pursuit of wage and hour violators.

[97] All agreed that she operated in a difficult political environment, with the effects of the Great Recession still being felt, Republicans staunchly opposed to labor-based initiatives, and the Obama administration's attentions focused elsewhere.

[109] As Supervisor for District 1, she was at the forefront of the response to the Exide lead contamination issue, which affected Vernon and several other communities within her purview and which touched upon her past concerns with environmental justice.

[120] In 2019, Solis, with fellow supervisor Sheila Kuehl, was a leader of the successful effort to stop a planned $1.7 billion mental health treatment center in the downtown area, intended to replace Men's Central Jail.

"[125] During the year, Solis also became an active supporter for Joe Biden's 2020 presidential campaign, saying that the former vice president, whom she dealt with during her time as Secretary of Labor, had the necessary "steady hand and experience" and who also is "personable" and can interact well with a wide range of people.

[128] As the pandemic in Los Angeles reached an especially high peak towards the end of the year, Solis pleaded with county residents to stay home: "As we near Christmas, I urge everyone to cancel their holiday plans to gather with members outside of one's households.

"[129] The pandemic subsequently ebbed for a while, but then by mid-2021 the highly infectious Delta variant had become a significant threat, and in July 2021 Solis issued an executive order reimposing an indoors mask mandate within the county.

Gavin Newsom requesting the phase out of the dangerous chemical Modified Hydrofluoric Acid (liable to cause a mass-casualty event in the case of a breach of its containment unit) at refineries where it remains in use rather than a safer alternative.

[30] In 2010, Solis received the inaugural Robert P. Biller Award for Exemplary Public Service from the University of Southern California's School of Policy, Planning, and Development.

[141] The Hilda L. Solis Care First Village is a set of housing units intended for the homeless that are put together using modular building techniques and located in Downtown Los Angeles.