The district includes South Bay and Westside regions of Los Angeles, as well as Beverly Hills, Santa Monica, the Palos Verdes Peninsula, and Beach Cities.

Lieu served on active duty with the United States Air Force Judge Advocate General's Corps from 1995 to 1999.

[3] Lieu joined the United States Air Force in 1995 and served four years on active duty as a member of the Judge Advocate General's Corps.

[2] Lieu continued to serve in the Air Force Reserve from 2000 to 2021; in this capacity, he was promoted to his terminal rank of colonel in December 2015.

On April 9, they were sworn in to replace outgoing members Marcia Cribb, Jack Messerlian, and Dan Walker, who had been elected mayor.

Lieu defeated three Republicans, including physician Mary Jo Ford and fellow Torrance city councilman Paul Nowatka.

In 2008, in a surprising turn of events in the Ladies Professional Golf Association (LPGA) English language controversy, Lieu and state senator Leland Yee of San Francisco were able to help rescind the LPGA Tour Commission's suspension-penalty policy for players who failed to learn enough English to speak to sponsors and at award ceremonies.

[11][12] Lieu is a strong supporter of expansion of public transit in West Los Angeles, LAX, and the South Bay.

[13] Lieu coauthored a successful bill to bypass environmental quality regulations to build a football stadium in Los Angeles.

The bill was intended to help the efforts of developer Edward P. Roski persuade the National Football League to return to the city, and was controversial among many environmentalists and legislators.

[15] As an assemblyman, Lieu authored laws in the areas of public safety, child sex offenders, domestic violence, the environment, education, health care, veterans' issues and transportation.

Lieu won a February 15, 2011, special election to fill the 28th Senate district following the death of incumbent Jenny Oropeza.

[24] The proposed bill asked California voters to repeal provisions of Proposition 209 and permit state universities to consider an applicant's race, ethnicity or national origin in making admissions decisions.

Lieu successfully passed three laws in the 114th Congress, securing $35 million in funding to the West Los Angeles VA for seismic retrofits; reauthorizing the Advisory Committee on Homeless Veterans; and restoring the Quarterly Financial Report.

[31] Lieu received praise from the online privacy community when he introduced bipartisan legislation to prevent states from forcing companies to weaken encryption for law enforcement purposes.

[32] On September 16, 2015, Lieu and Justin Amash introduced a bill[33] to reduce funding for the Drug Enforcement Administration's Cannabis Eradication Program,[34] under which real estate and chattels can be seized if they have been used for marijuana trafficking and abuse.

[citation needed] On November 6, 2017, while the House of Representatives chambers was holding a moment of silence was held for the 26 victims of a church shooting in Texas, Lieu filmed and posted a video message calling for gun law reform.

[37] On April 25, 2018, 57 members of the House of Representatives, including Lieu,[38] released a condemnation of Holocaust distortion in Ukraine and Poland.

[38] In 2019, Lieu signed a letter led by Representative Ro Khanna and Senator Rand Paul to President Trump asserting that it is "long past time to rein in the use of force that goes beyond congressional authorization" and that they hoped this would "serve as a model for ending hostilities in the future—in particular, as you and your administration seek a political solution to our involvement in Afghanistan.

[69] In 2012, Lieu authored a bill[70] that bans the provision of sexual orientation change efforts (including conversion therapy) to minors.

This bill passed both the State Assembly and Senate with substantial support, and was signed into law by Governor Jerry Brown in 2012.

[72] As U.S. representative, Lieu has introduced the Therapeutic Fraud Prevention Act, a bill for a federal ban on conversion therapy, following statements by President Obama opposing the practice.

[73] Lieu supports banning hydrofluoric acid (HF) at oil refineries, where it is often the chemical used for producing the high octane alkylate component of gasoline.

[82] In 2023, after the release of ChatGPT, Lieu wrote in the New York Times to call for regulation of artificial intelligence, arguing that "Failure to do so could lead to a future where the risks of AI far outweigh its benefits.