McGuire was elected to the HealdsburgCity Council in 2004, where he spent six years, including time as the city's youngest mayor.[6] In 2010, he became a member of the Sonoma CountyBoard of Supervisors.[7] In 2014, McGuire easily defeated Republican candidate Lawrence Weisner for the District 2 State Senate seat, winning 70% of the vote.[8]
In April 2015, he introduced bill SB 643, with the purpose of legalizing and regulating the medical marijuana industry.[9] The regulation would cover cultivation to consumption.[10] McGuire criticized the state's lack of rules and regulations for medical marijuana,[11] and was opposed to the Adult Use of Marijuana Act (Proposition 64).[12] In September 2017, he was part of the state's legislative session that urged Congress to censure the president Donald Trump.[13]
In September 2018, the bill he introduced to establish a statewide protocol for emergency alerts for all 58 California counties was signed into a law.[14] In December 2018, he was selected to serve as assistant majority leader of the California Senate.[15][16] In early January 2019, Mike McGuire "applauded" Gavin Newsom's 2019 budget plan for California.[17] That same month, when president Donald Trump threatened to withhold government emergency fundings for the wildfires because of poor forest management by the state of California, Mike McGuire replied in a tweet that most California forests affected are managed by the federal government and not the state.[18]
In 2019, he co-authored California Senate Bill 27 (SB27) officially named Tax Transparency Bill which was signed into law by Governor Gavin Newsom on July 30, 2019.[19]
