In 2001, Kennedy served on the Committee to Elect Sarah Marsh to the U.S. House of Representatives. In 2002, she became the Green Party of Arkansas's elections co-chair; she held this position until 2007 when she became the party's public relations co-chair. In 2008 she relinquished the latter position to return to being elections co-chair.

Beginning in 2004, Kennedy practiced law as an associate of the firm of Pryor, Robertson, Beasley & Smith in Fort Smith. Her practice includes work in the area of civil rights and on behalf of victims of discrimination in the workplace. In 2008, Kennedy departed from the firm and founded the Law Office of Rebekah Kennedy.

Kennedy was perhaps best known for her 2006 bid for Arkansas Attorney General, which garnered 4.4% of the vote.

In 2008, the Republican Party declined to nominate a candidate in the 2008 Senate election in Arkansas. Thus, Kennedy became the sole challenger of Democratic Senator Mark Pryor in his first race as an incumbent. Kennedy received a 206,504 votes for 20.54% of the vote . This is the highest percentage of the vote for any Green Party candidate running for U.S. Senate ever, and her 206,504 votes is the second most total votes received by a Green Party candidate for U.S. Senate. Kennedy's campaign, in addition to being record breaking for the Green Party, was also the strongest showing of any independent or third party candidate running for the U.S. Senate in 2008.

Kennedy unsuccessfully ran for the office of Attorney General in the 2010 election cycle as the Green Party nominee. She faced one-term Democratic incumbent, Dustin McDaniel; the state Republican Party did not field a candidate. She received 193,658 votes, or 26.79%.

In 2012, Kennedy challenged Rep. Steve Womack for the U.S House of Representatives in a race that had no Democrat. She came in second out of 3 candidates, receiving 39,318 votes, or 16.01%.