McKinney was first elected to the House in 1992, after previously serving in the state legislature. A decade later, she was defeated in her 2002 Democratic primary by Denise Majette, after she had made public remarks aligning herself with the nascent conspiracy theorists who would come to be known as the 9/11 Truthers -- questioning whether the Bush administration knew about the 9/11 attacks beforehand, and allowed them to happen in order to benefit key business interests.
She then regained her seat in 2004, when Majette ran unsuccessfully for Senate. But she lost it again in 2006 to Democrat Hank Johnson, who still holds the seat, who was able to win in an upset after an incident occurred in which McKinney was accused of punching a Capitol Hill police officer.
In 2008, she switched to the Green Party, becoming its presidential nominee, receiving only about 160,000 votes and just over 0.1% of the national popular vote. (Former 2000 Green Party nominee Ralph Nader, running as an independent, received almost 740,000 votes, for under 0.6% of the vote.)