After Cincinnati Bengals' quarterback Greg Cook was injured during the 1970 preseason, Carter was traded by the Bills to the Bengals in exchange for a draft choice. He led the NFL in pass completion percentage in 1971 and was third in overall passing. His best game of that season was the opener, in which the Bengals defeated the Philadelphia Eagles 37–14.
When Cincinnati Bengals quarterback Greg Cook got hurt during the 1970 training camp, Carter was swapped by the Bills for a draft selection. He topped the NFL with pass completion percentage in 1971 and ranked third overall in passing. His standout game that year was the season opener, where the Bengals thrashed the Philadelphia Eagles 37–14.