2020 United States Senate special election in Arizona

The 2020 United States Senate special election in Arizona was held on November 3, 2020, following the death in office of incumbent Republican U.S. Senator John McCain on August 25, 2018. Governor Doug Ducey was required by Arizona law to appoint a Republican to fill the vacant seat until a special election winner could be sworn in. On September 5, 2018, Ducey appointed former U.S. Senator Jon Kyl to fill McCain's seat. However, Kyl announced he would resign on December 31, 2018.

On December 18, 2018, Ducey announced that outgoing U.S. Representative Martha McSally would be appointed to fill the seat following Kyl's resignation. McSally was sworn in as the state's junior U.S. Senator on January 3, 2019, less than two months after she was defeated by Democrat Kyrsten Sinema for Arizona's Class 1 U.S. Senate seat. McSally ran to complete the term, defeating skincare executive Daniel McCarthy in the Republican primary. She faced former astronaut Mark Kelly, who ran uncontested in the Democratic primary. Primary elections took place on August 4, 2020.

Once a reliably Republican state, Arizona trended more purple in the late 2010s. Kelly significantly outraised McSally and led by about 5% in the average poll leading up to Election Day.

Kelly defeated McSally by a margin of 2.4% on election night, thereby flipping the seat Democratic. As a result, he outperformed Joe Biden in the concurrent presidential election, who defeated President Donald Trump by a margin of 0.3% in the state, but underperformed his polling average. Kelly became the first Democrat to win the Class 3 Senate seat since Carl Hayden won his last term in 1962.

Kelly was sworn in on December 2, 2020, marking the first time since 1953 that Democrats held both of Arizona’s Senate seats.