Mariah Willoughby was a 23rd century Human woman. In the mid-2260s, Willoughby served as an officer in Starfleet, working as an aide to Admiral Saylor aboard Starbase 33.
In late 2265, Lieutenant Willoughby welcomed the USS Enterprise when the starship arrived at Starbase 33, she also informed Captain James T. Kirk that Saylor would like to see him at his earliest convenience. When Kirk transported aboard the starbase, Willoughby welcomed him in the transporter room, and escorted him to the briefing with Saylor. (TOS - My Brother's Keeper novel: Constitution)
After several months petitioning for a starship assignment, her first since Starfleet Academy training simulations, Willoughby was finally offered a posting aboard the USS Defiant under the command of Captain Serling, which she accepted. When accompanying Kirk back to the transporter room at the conclusion of his debriefing, she asked him about serving aboard a starship and about Captain Serling. She was due to transfer a week later. (TOS - My Brother's Keeper novel: Constitution)
- Willoughby was described as wearing full lieutenants band on her uniform which suggests that Starbase 33 had rolled out the new Starfleet uniform, as opposed to the older uniforms which used a single gold band to represent all officer bands, except captain.
- It is unknown if Willoughby was still serving aboard the Defiant when it became trapped in an interphase in 2268, during which the entire crew perished.
