Mac was one of the original raw recruits from Danny Franks unit, inscripted into Bad Company along with him and Trucker. He became close friends of Danny and managed to survive the final battle at Ararat along with Danny and Mad Tommy.
He was part of the 2nd incarnation of Bad Company, but just after recruting Sheeva, he stood on a shell which blew his arm off. In between Bad Company - The Bewilderness and Bad Company - The Krool Heart, Mac had an artificial arm put on.
Mac also survived the final attack on Krool and was there to witness Danny Franks take over the Krool Heart. It is not known what became of Mac after that, but seeing as Kano ended up settling down on a planet, it's likely that Mac too decided to settle down somewhere too and he did not return in the 3rd incarnation of Bad Company.