Ripley, 45, succeeds another former Northamptonshire player in David Capel, who parted company with the county after 33 years last month. He had previously operated as second XI coach and academy director before temporarily taking charge of the senior side on Capel's departure.
Northamptonshire cricket chief executive David Smith said: "There is little doubt the environment at the club has changed significantly since David has taken over."
He added: "A good dressing room is important for player retention and new player recruitment, as is a sense of belonging and what the club stands for.
"David has impressed everyone in how he has handled all elements of the job since taking over in early July."
Phil Rowe has been appointed into Ripley's former role.
Ripley played for Northamptonshire from 1984 to 2001 and scored 8,693 first class runs with nine centuries, in addition to 678 catches and 85 stumpings.