Re-elected in 1974, Mitchell ran for Mayor of Tempe in 1978, gaining a majority of votes cast in the primary and avoiding a runoff.

Four years later, however, Mitchell sought and won a seat in the Arizona Senate, representing Tempe and parts of southern Scottsdale.

One year later, with the 2006 midterm elections approaching, Mitchell ran unopposed for chair of the Arizona Democratic Party after chairman Jim Pederson stepped down to run for the United States Senate.

Mitchell oversaw much of the early ground work as the Arizona Democratic Party prepared for statewide elections on November 7, 2006.

[3] He has voted for legislation largely supported by Democrats in Congress, such as the State Children's Health Insurance Program.

Although he expressed reservations about many of the provisions of the Patient Protection and Affordable Care Act,[4] he ultimately voted for it.

Stating it was a "matter of principle," he declined coverage under the Federal Employees Health Benefits Program in favor of Medicare.

Hayworth would be in a tight race against any of a handful of Democratic opponents; the district was rated "Toss-Up" by the Cook Political Report.

Mitchell was pressured by several Arizona politicians and Rep. Rahm Emanuel, then head of the DCCC, to enter the race against Hayworth.

On the evening of November 7, election day, most national and state news media outlets declared Mitchell the winner.

Mitchell was reelected in 2008 with 53% of the popular vote over his Republican challenger, former Maricopa County treasurer David Schweikert.