The 34-year-old was confirmed for the managerial position following his interview with new club owner Alan Hardy on Thursday.
County have lost their last ten league games and sit just a point above the relegation places and former Leyton Orient player-manager Nolan will be aiming to stop the rot at Meadow Lane.
Hardy said of the ex-Bolton Wanderers and Newcastle United star: "I have spoken to five managers in the last five days and Kevin Nolan is outstanding, and that's what this club needs.
"I will provide the leadership off the pitch and he will provide it on the pitch.
"Not only is he still a good footballer but at Leyton Orient he had immediate success and that is important for us because we need to start winning games and climbing the table and get away from relegation zone."