Alex Padilla

On April 11, 2013, Padilla announced his intention to run for California secretary of state in 2014, to succeed the term-limited incumbent Debra Bowen. He was expected to face an intraparty battle with fellow Democrat Leland Yee, but Yee's arrest for felony racketeering caused Yee to abandon the race. Padilla won the election on November 4, 2014, with 53.6% of the vote, defeating Republican Pete Peterson. He was officially sworn into office specifically on January Monday 5, 2015, concurrently during Jerry Brown's fourth term.

On June 29, 2017, the Presidential Advisory Commission on Election Integrity, which President Donald Trump created on May 11, requested data on enrolled voters from every state, dating back to 2006. Padilla said that California would not supply the data.

On November 6, 2018, Padilla was reelected with 64.5% of the vote, defeating Republican Mark P. Meuser.

On October 16, 2020, Padilla was involved in a controversy between the state and the California Republican Party, as the party deployed unofficial ballot boxes for voters to submit their ballots at select locations, including churches and gun stores in competitive California districts. Padilla issued a cease-and-desist order, arguing that the ballot boxes were illegal and failed to ensure ballot security. Local Republican leadership refused to follow the order and said the boxes were a form of legal ballot harvesting that had been enabled by recent Democratic legislation (which lacked a chain of custody requirement), and were a way to increase voter turnout. Accusing Democrats of hypocrisy given their widespread door-to-door ballot harvesting in the 2018 United States elections, the state Republican Party later agreed to a set of collection procedures and said a volunteer's mistake of affixing a sign denoting the ballot box as "official" had contributed to the political standoff; Padilla's office said it was continuing to investigate whether ballots were being handled correctly and that the "ineptitude or unlawfulness of a political operative or campaign volunteer" could nonetheless lead to "serious legal consequences".

In early 2020, Padilla announced a $35 million no-bid contract for a statewide voter education ad campaign with partisan public relations firm SKDK (then known as "SKDKnickerbocker") called "Vote Safe California", but State Controller Betty Yee blocked the funding because Padilla's office did not have the authority to use federal money that was allocated to county governments; the campaign proceeded anyway. The group had marketed itself as being on "Team Biden", and the awarding of the no-bid contract under supposed "emergency powers" despite the group's ties with the Democratic Party and work for Democratic politicians running for office in California received bipartisan criticism. Amid ongoing litigation by the Howard Jarvis Taxpayers Association, who contend that the contract bypassed fair competition rules and misappropriated federal election funding for local elections operations, and was therefore illegal, Governor Newsom signed legislation that provided state funding to reimburse SKDK in February 2021.

Upon Padilla's appointment to the U.S. Senate, Newsom appointed Assemblywoman Shirley Weber to succeed him.

In August 2020, Democratic presidential nominee Joe Biden selected California Senator Kamala Harris as his running mate. After they won the general election, Padilla was mentioned as a possible choice as Harris's successor in the Senate. Governor Newsom had the power to appoint her successor. In December 2020, Newsom announced that he would appoint Padilla to the seat, making him California's first Hispanic senator and the first male U.S. senator from California since Alan Cranston retired in 1993. During the speculation about whom Newsom would appoint, the senior senator from California, Dianne Feinstein, supported Padilla. To replace Padilla as California's secretary of state, Newsom appointed state assemblywoman Shirley Weber.

Most Latinos, who are 40% of California's population, supported Padilla's appointment, but some black leaders, who wanted another black woman to replace Harris, criticized it. San Francisco Mayor London Breed called Padilla's appointment "a real blow to the African American community".

Padilla announced that he would seek a full term in 2022. He appeared on two ballots: one for the special election to fill the remainder of his term in the 117th Congress, and the other for the new term beginning with the 118th Congress. The special election was due to a recent change in California law that ended Padilla's appointment in November 2022. He was on the ballot in two separate races in the November 2022 election—a special election for the final two months of Harris's Senate term, and a regular election for a full six-year term beginning in January 2023.

On January 20, 2021, Padilla was sworn into the United States Senate in the 117th Congress by Vice President Kamala Harris, his predecessor, becoming the first Latino to represent California in the U.S. Senate. He was sworn in by Vice President Harris on her first day, at the same time as new Georgia senators Jon Ossoff and Raphael Warnock. He served the final two years of Harris's term. He filed the necessary paperwork with the FEC to run for a full term and an unexpired term in the 2022 elections which he won in November 2022.

While in office, Padilla introduced legislation to add more legal protections for various public lands in California, including parts of the San Gabriel Mountains, Los Padres National Forest, and Carrizo Plain National Monument. Padilla also introduced legislation to help coastal communities adapt shorelines to increased flooding and erosion from sea level rise and extreme weather.

As of the end of 2023, Padilla had voted with Biden 100% of the time.

• Committee on the Judiciary
  • Subcommittee on Criminal Justice and Counterterrorism
  • Subcommittee on Federal Courts, Oversight, Agency Action and Federal Rights
  • Subcommittee on Immigration, Citizenship, and Border Safety (Chairman)
  • Subcommittee on Intellectual Property
  • Subcommittee on Privacy, Technology and the Law
• Committee on the Budget
• Committee on Environment and Public Works
  • Subcommittee on Clean Air, Climate and Nuclear Safety
  • Subcommittee on Fisheries, Water, and Wildlife (Chair)
  • Subcommittee on Transportation and Infrastructure
• Committee on Energy and Natural Resources (since October 2023)
• Committee on Rules and Administration

• Committee on Homeland Security and Governmental Affairs (until October 2023)

• Congressional Hispanic Caucus
• Senate Cultural Caucus
• Congressional Asian Pacific American Caucus
• Rare Disease Caucus

• National Security Commission on Emerging Biotechnology, Commissioner

The Wall Street Journal says that Padilla had "a reputation [in the State Senate] as a business-friendly moderate". FiveThirtyEight defined him as a technocrat, not identified with either the progressive or the moderate wing of the party. The American Conservative Union gave Padilla a 0% rating in 2012. On January 18, 2021, Padilla released a statement in support of the Green New Deal and Medicare For All legislation, among other progressive policies.

Padilla favors abortion rights, saying in 2018 that abortion rights are "not negotiable". In 2008, Padilla sponsored the bill SB 1770, which would require the Commission on Peace Officer Standards Training (POST) to prepare relevant guidelines and mechanisms for the investigation and reporting of "cases involving anti-reproductive-rights crimes". In 2018, after winning the primary for secretary of state to seek a second term, he received support from NARAL Pro-Choice America.

When Roe v. Wade was overturned in June 2022, Padilla condemned the decision.

Padilla supports transgender rights.

Padilla supports climate action and said during budgetary discussions in October 2021 that "[c]limate cannot be on the chopping block in this or any budget." He supports the Green New Deal and has said that it "offers a once-in-a-generation opportunity." Padilla received a 100% score from the League of Conservation Voters in 2021.

Padilla supports ending the Senate filibuster.

Padilla supports immigrants' rights. On January 15, 2021, he said that he supports legislation sponsored by representative Joaquin Castro to speed up the citizenship process for undocumented immigrants in essential jobs, declaring that because of the work they do, "they deserve stability".

Padilla has been known for efforts to expand voting access. When he was appointed to the Senate in 2021, Newsom called him "a national defender of voting rights".

In November 2023, Padilla introduced legislation in the Senate to authorize a binding federally sponsored referendum, known as a plebiscite, to resolve Puerto Rico's political status. The legislation details the transition and implementation of non-territorial status for Puerto Rico: statehood, independence, or sovereignty in free association with the U.S.

Padilla voted to reauthorize the Foreign Intelligence Surveillance Act.