Marlow was a CIA agent and a former associate of Jack Bauer. Jack called him his specialist and indicated he was great at finding out information very quickly.
During Day 9, Marlow was stationed at CIA Headquarters in Langley, Virginia. At around 7:40pm GMT, Bauer called Marlow and sent him the fingerprint of the assassin that had killed CIA technician Jordan Reed as he was unable to identify the man himself. Marlow started running the fingerprint through several databases and identified him as James Harman, a former CIA deep-cover operative and assassin. Trying to figure out who could have hired Harman, Jack had Marlow read the names of Harman's handlers. Marlow identified Steve Navarro as one and as Navarro was the Station Chief Jack was working with, he realized that Navarro was the one who hired the killer. While Marlow's help exposed Navarro's treachery and helped solve Jordan's murder, it was too late as Navarro knew that Jack was getting Marlow to help him and fled with the defense override module. ("Day 9: 7:00pm-8:00pm")