|Played by:||Jayne Atkinson|
|First episode:||Day 5 7:00pm-8:00pm|
|Last episode:||Day 6 9:00am-10:00am|
Karen Hayes was the head of the Department of Homeland Security during the events of Day 5 and was called in to take control of CTU. By Day 6 she became the National Security Advisor and married Bill Buchanan.
Before joining the Department of Homeland Security, Hayes was an FBI agent. She worked within the FBI's Counterterrorism Division, eventually becoming Senior Agent and later a Division Agent in Charge.
Hayes has a Bachelor of Arts in Sociology from Princeton University.
After Sentox VX nerve gas was released onto CTU, Hayes was sent by President Charles Logan and Vice President Hal Gardner to take control of CTU. She and her assistant Miles Papazian planned to make massive changes to CTU's staff.
Hayes finally told Bill Buchanan that CTU was set to be absorbed by Homeland Security. Although he did not interfere with her plan, she and Miles had Audrey Raines sign a statement blaming him for the day's events.
Hayes is told by President Charles Logan that there is a warrant out for the arrest of Jack Bauer. While Hayes doesn't feel right diverting resources from finding Christopher Henderson, she reluctantly agrees to help track Bauer down, hoping Audrey would lead her to Bauer.
However, when Hayes' field units are called off from bringing in Bauer, she begins to question the orders she is getting. She calls Mike Novick directly to ask about Logan's orders. This leads her to suspect that Logan may not be acting in the countries best interests. After Shari Rothenberg tells Karen that Chloe O'Brian said that President Logan was involved in the day's attacks, Karen begins to realize what is happening, and calls Bill to tell him that a team is on the way to capture Chloe for helping Jack Bauer. Chloe is able to escape, and Karen brings Bill to CTU to secretly help Jack acquire evidence against the president.
She eventually brings Chloe into CTU to help, and Miles becomes more and more suspicious. After Karen, Bill, and Chloe help Bauer return to CTU, Karen is forced to tell Miles about the situation with President Logan. Miles betrays Karen and destroys the recording implicating President Logan, and he leaves CTU, but not before Karen slaps him.
Karen continues running CTU, and helps with the operation to stop Vladimir Bierko. After President Logan is finally taken down, Bill Buchanan asks Karen out to breakfast. Karen tells him that she has a mandatory briefing at division, but asked him for a rain check. He accepted.
Between Day 5 and Day 6, she and Bill Buchanan got married.
She was promoted to National Security Advisor sometime after Day 5 as well. In that position, she strongly opposes Thomas Lennox and his idea to use racial profiling and put all Muslims in detention centers to prevent any further terrorist attacks.
- Karen: Your emotional involvement with Miss Raines is not exactly a secret, Jack.
- Jack: That has nothing to do with this!
- Karen: That's right. You always put the work first, you never let your feelings get involved. Is that what happened with Nina Myers?