(coexisting on another dimensional plane)
With Captain Forrest in the brig, Archer ordered Mayweather to search Forrest's personal files for messages from Starfleet which may have provided the identity of a potential spy planted aboard Enterprise. Forrest threatened Mayweather that if he obeyed Archer he would be executed as a co-conspirator. Mayweather ignored him and carried out Archer's order.
It was Mayweather who alerted Archer when the Tholians constructed an energy web in Defiant's path to prevent their escape, though their efforts were futile. Following the Defiant's escape, Mayweather was present in a conference in the ship's briefing room regarding the status of the ship's warp drive. Afterward, Archer grabbed Mayweather's particle rifle and aimed it at T'Pol, threatening to kill her for betraying him.
Archer had Mayweather severely beat alien workers found aboard the Defiant to learn who was responsible for the theft of a pair of plasma regulators and the murder of Ensign Kelby. Mayweather then participated in the hunt for Slar, the Gorn slave master who was responsible for said thefts and killings.
After Major Malcolm Reed was severely injured by Slar, Mayweather assumed the duties of weapons officer, manning the Defiant's helm console. As such, he operated the Defiant's advanced weaponry during the ship's battle with a fleet of Vulcan, Andorian, and Tellarite ships rebelling against the Terran Empire.
Later, Mayweather assisted Archer in murdering Admiral Black when Black refused to promote Archer and grant him command of the Defiant on a permanent basis. Mayweather killed Black's bodyguard, allowing Archer to kill Black with a phaser. Later, when Archer relieved T'Pol of her duties aboard Defiant, Mayweather confiscated her phase-pistol and her dagger.
Mayweather was manning the helm when Phlox began sabotaging the Defiant's warp drive. Mayweather reported on the fluctuations in the warp field and was preparing to alert Archer, but Tucker stopped him, explaining that it was likely not important enough to warrant interrupting the captain. Mayweather was still at the helm when the ship's systems began to fail and the ISS Avenger began attacking the ship. Power was ultimately restored, and Mayweather destroyed the Avenger on Archer's orders.
As it turned out, Mayweather had been secretly plotting the takeover of the Defiant with Hoshi Sato, having become her consort. Mayweather helped Sato poison Archer, allowing her to take command of the Defiant and issue her ultimatum to Fleet Admiral Gardner. (ENT: "In a Mirror, Darkly, Part II")