Born in South Africa on Earh, Sloan graduated from a satellite campus of Starfleet Academy in 2360. Due to the opposition of Starfleet Intelligence head Nyota Uhura Sloan was unable to advance within SI, and was instead recruited in to Section 31.
By 2374 Sloan was a director in Section 31. He led a project within Section 31 to engineer the morphogenic virus to commit genocide against the Founders of the Dominion.
Also in 2374 he attempted to recruit Dr. Julian Bashir into Section 31 by kidnapping the man and subjecting him to a holographic simulation designed to gauge his loyalty to the Federation. Bashir eventually realized he was in a simulation when the simulation of Chief Miles O'Brien did not have a dislocated shoulder. Bringing the simulation to an end, Sloan was satisfied that Bashir was loyal to the Federation and tried to get Bashir to join Section 31, but Bashir refused the invitation.
Sloan tried to get Bashir to help him during a medical conference on Romulus by letting him on plans that he intended to assassinate Chairman Koval of the Tal'Shiar, knowing that Bashir would try to warn the Romulans through Senator Cretak. When Cretak accessed Koval's personal data in an attempt to stop Sloan, she was arrested and expelled from the continuing committee of the Romulan Empire, and Koval was named to take her place. The whole thing turned out to be a ruse concocted by Sloan and Admiral Ross to ensure that Koval - a Federation mole - was named to the continuing committee.
Upon learning that Sloan and Section 31 had engineered a virus to destroy the Founders of the Dominion, Bashir lured Sloan to the station, knowing the Section 31 leader would probably have the information for the cure. When Sloan turned up in Bashir's quarters, Bashir stunned Sloan and hooked him up to Romulan Mind Probes. Despite Sloan's activating a suicide implant to stop Bashir from getting the information, Bashir was able to retrieve the information from Sloan before he died. With that information Bashir was able to cure Odo of the disease. In turn Odo was able to cure the Female Changeling and the rest of his race upon his return to the Great Link.