He studied Political Science at the University of California Berkeley, and went on to serve on the Berkeley Housing Commission and Rent Stabilization Board before his election to Berkeley City Council in December 2008. He represented District 4 on the council until his election on November 8, 2016 as the first Latino and youngest person to serve as the city’s mayor.
Arreguin represents the cities of Alameda County on the Executive Board of the Association of Bay Area Governments. He also represents Berkeley on the Board for the East Bay Community Energy Authority, and the Alameda County Waste Management Authority, and chairs the Council's Agenda Committee, 2x2 Joint City/School Board Committee, 3x3 Joint Housing Authority/Council Committee; and 4x4 Joint Committee on Housing.
Arreguin was born in Fresno, California and grew up in San Francisco, California. His parents and grandparents were farmworkers. At age 9, Arreguin became involved in the ultimately successful campaign to change the name of Army Street to Cesar Chavez Street in the historically Latino Mission District of San Francisco. Arreguin continued to be involved through efforts against reverse the name change in 1995, described as having “campaigned tirelessly to keep one of the Mission’s main thoroughfares named after his idol, Cesar Chavez...”
Arreguin was the first in his family to attend college, and graduated from the University of California Berkeley with a degree in Political Science in 2007. While attending UC Berkeley, Arreguin served as the City Affairs Director for the Associated Students of the University of California and was elected to the Berkeley Rent Stabilization board in 2004, serving as chair through 2008.
Arreguin has also served on the Housing Advisory Commission, Zoning Adjustments Board, and Downtown Area Plan Advisory Committee.
Berkeley City Councilmember
From 2008 to 2016, Arreguin served two terms as a Berkeley City Council member representing City Council District 4. On the council, Arreguin drafted and passed over 300 pieces of legislation.
He helped increase the city’s minimum wage to $15, co-wrote the Downtown Area Plan, pass the Affordable Housing Mitigation Fee, used to build affordable housing, create police reform after Black Lives Matter demonstrations, and worked to save the historic Main Post Office.
Mayor of Berkeley
Arreguin announced his candidacy for Mayor of Berkeley in October 2015. He faced seven candidates for the open Mayor’s seat, and was endorsed by U.S. Senator Bernie Sanders of Vermont, the Sierra Club, and the Alameda Democratic Party.
Arreguin won 51% of the vote after ranked-choice tabulation. Prior to his swearing-in, Arreguin vowed as Mayor-elect alongside City Council members that “Berkeley would remain a sanctuary city and continue to shield its undocumented residents from deportation.”  Arreguin was sworn in as Mayor on December 1, 2016 and in his inaugural address said that “in light of the national election, Berkeley, now more than ever, needs to lead.” 
In January 2017, following the release of Donald Trump’s executive orders calling for the construction of a border wall, and enforcement of immigration law including the withholding of federal funds from sanctuary cities, Arreguin released a statement along with other progressive mayors in the region opposing the “hateful and harmful policies.” 
When a talk by controversial “alt-right” commentator Milo Yiannopoulos was announced on the University of California, Berkeley campus in February 2017, Arreguin commented that “Bigotry is unacceptable. Hate speech isn’t welcome in our community.” After violent protests caused UC Berkeley to cancel the talk, Arreguin stated that “we as a city do not make a decision about inviting a speaker. We do not make a decision to cancel a speaker. This was a decision of the university." 
In response to the same incident, Arreguin referred to Yiannopoulos as a “white nationalist,” but later retracted his characterization of Yiannopoulos, and instead described him as an “alt-rightist.”  Arreguin began receiving death threats by Yiannopoulos supporters from across the country after his statements were covered by far-right news website Breitbart News, Yiannopoulos’s employer at the time.
With Arreguin’s backing, the Berkeley City Council voted in March 2017 to divest from companies involved in constructing the proposed border wall with Mexico, becoming one of the first cities in the country to do so. The City Council also passed a resolution calling for the impeachment of Donald Trump, co-sponsored by Arreguin, who stated that “[e]very day there’s a new ethical problem that warrants impeachment.”
Arreguin again became a target of death threats when conservative commentator Ann Coulter planned to speak on the UC Berkeley campus and canceled her appearance over legitimate safety concerns in April 2017. During protests over Coulter’s appearance, Arreguin was denounced for supporting the far-left group BAMN (By Any Means Necessary), which has incited violent protests, after it became known that he had “liked” their Facebook page. In response, Arreguin said that “following or liking pages does not mean you support what that group is doing,” adding, “I am not a member of BAMN, and I do not support the views and the violent actions of that group.” He later un-followed the group.
In May 2017, Arreguin co-sponsored the successful resolution to divest the City of Berkeley from Wells Fargo Bank in response to allegations that the bank opened fraudulent deposit accounts, the bank’s financing of private prisons and the Dakota Access Pipeline.
After President Trump’s withdrawal of the United States from the Paris Agreement in June 2017, Arreguin pledged along with 350 other mayors “to uphold the Paris Agreement goals even though President Donald Trump pulled the U.S. out of the international agreement to combat climate change.” 
Following the Charlottesville Unite the Right rally, attention was brought to a planned far right rally planned for August 27 in Berkeley. Ahead of the event, Arreguin stated that his office was “currently exploring all options, including whether we have the legal means to stop this rally from taking place.”  At a press conference with local leaders including Rep. Barbara Lee and State Sen. Nancy Skinner, Arreguin called for opponents of the rally to hold counter-demonstrations in different locations to avoid violence between groups.