The Bills made the move Wednesday.
The six-foot-five, 323-pound Charles, a native of Oshawa, Ont., joined the Bills after spending the first eight weeks of the season on the Tennessee Titans' practice roster.
Charles signed with Tennessee after being bypassed in last year's NFL draft.
The former University of Regina star was selected in the second round, 10th overall, in the 2013 CFL draft by the Edmonton Eskimos.
Charles appeared in 20 games at Regina, registering 9.5 sacks and 74 tackles.