Castor entered the race for what was then the 11th district when five-term incumbent Jim Davis chose to run for governor (he lost to Charlie Crist in November).

Castor was endorsed by the pro-choice political action committee EMILY's List, the League of Conservation Voters, Oceans Champions, The Tampa Tribune, The St. Petersburg Times and The Bradenton Herald.

[6] Christine Quinn, the founder of My Family Seasonings, challenged Castor instead, running on a pro-business and anti-immigration platform.

The Bush plan does not provide sufficient help to middle-class families in the housing squeeze or taxpayer protections.

"[24] In Tampa Bay, Recovery Act funds were invested in transportation, education, housing, research, law enforcement and various local infrastructure improvements.

[25] The I-4/Crosstown Connector received the largest Recovery Act investment in Tampa Bay, with $105 million to make completion of the project possible.

[27] In June 2021 of the 117th Congress, Castor joined 267 of her colleagues in voting to repeal the Authorization for Use of Military Force (AUMF) Against Iraq Resolution of 2002.

Today’s vote is a first step in ensuring that the AUMF will not be used by any president to justify new and unrelated offensive military actions.

By finally repealing this two-decade old AUMF, this legislative body can once more execute its solemn constitutional responsibility, focus on supporting our service men and women and end the blank check for war."

Castor has called the GI Bill for the 21st century that passed in 2008 despite strenuous opposition by President Bush "one of the most important pieces of legislation that I have cosponsored.

[citation needed] In 2008, Castor successfully championed legislation to allow low-income families with overdue medical bills to still be eligible for student loans.

[citation needed] Since the Affordable Care Act passed, Castor has worked to educate Floridians about new patient protections and rights, and about enrollment in the marketplace exchange.

[32] She was critical of Governor Rick Scott and the Republican-led Florida legislature for not accepting more than $50 billion in federal funding to expand Medicaid to provide health care access to more than one million Floridians.

In 2005, she was the lone Hillsborough County commissioner to vote against a resolution to ban gay pride activities and events.

After the 2016 Pulse nightclub shooting, she participated in John Lewis's Congressional sit-in to demand that those on the No Fly List lose the right to purchase firearms.

"[41] In the wake of the Stoneman Douglas High School shooting, Castor reiterated her support for repealing the Dickey Amendment of 1996, which discourages funding to the CDC to research gun violence prevention.