McAvennie was a peace officer who worked for Babylon 5 security.
In 2261, when the Thirdspace artifact arrived at the station, McAvennie was guarding Babylon 5's Maintenance room. When a Vorlon-controlled Lyta Alexander tried to break into Maintenance, attempting to ram the artifact with the Maintenance Bots, she incapacitated McAvennie with her telepathic abilities.[1]