Following the Fourth Succession War, Archibald McCarron took a leave of absence from commanding McCarron's Armoured Cavalry to handle recruitment and deal with their supply issues. Previous to this it is believed that he served with their Second Regiment, Barton's Regiment. Marcus Baxter was the man he chose to take command in his absence and when Archibald returned in 3037, he was able to raise a sixth regiment 'Baxter's Brawlers' and placed Marcus in command of it.
After the death of Archibald during a training accident in 3050, the close-knit group elected Marcus to take command of the mercenary brigade. Marcus later married Archibald's widow and adopted his two children, Rhamses and Faith McCarron, who will eventually take command of the unit. With the beginning of the Xin Sheng movement, he accepted the offer of Sun-Tzu Liao for CCAF sponsorship to become a household unit on the eve of the Capellan-St.Ives War. By accepting the offer, he insured Citizenship in the Capellan Confederation for himself and each member of his unit. Baxter commanded the unit in heavy combat in 3057 during the Marik-Liao offensive and again during the war against St. Ives in 3060. During the Word of Blake's Jihad, the "Big Mac" was thrown into almost every major offensive. Although the "Big Mac" has a sorted history with Wolf's Dragoons, after the Word utterly annihilated the Dragoons, Marcus has made a concerted effort to reach out to any surviving Dragoon members left straggling after the fighting on Outreach. While there is little love lost between the two units, Baxter's begrudging respect for the Dragoons makes him empathetic to their plight, as he personally believes such a historic unit deserves a more glorious ending. By recruiting new members into the "Big Mac" exclusively from the St. Ives Commonality, Baxter believes that he can in some small way make St. Ives Citizens feel part of the Confederation as a whole, further helping to unify the nation. Currently, he is the Mandrinn of Menke and Mitchel. He remains in command and coordinates all efforts of the units from Menke.
In "Masters and Minions", Marcus' last name is stated as "Baxter". However, in "McCarron's Armored Cavalry" (BattleTech 1669), there is a "Marcus Barton" stated as being the regimental commander. Clarification is needed.
- "McCarron's Armored Cavalry" (BattleTech 1669)lists both a "Marcus Barton" and a "Marcus Baxter".
- Marcus Barton is the commander of MACs 2nd regiment "Barton's Regiment" (BattleTech 1669) p. 11
- Marcus Baxter is the commander of MACs 6th regiment "Baxter's Brawlers" formed in 3037 (BattleTech 1669) p. 10