The big striker scored the decisive second goal as the Canaries saw off the plucky challenge from the bottom side to remain nine points clear at the top with just six matches to play.
Norwich took less than three minutes to go in front, Anthony McNamee beating keeper Owain Fon Williams with a fine chip from just outside the area to record his first goal for the club.
The Hatters reacted in the best possible fashion by levelling nine minutes later. Stand-in keeper Declan Rudd, did well to block an effort from Ritchie Partridge but the ball fell kindly for striker partner Jabo Ibehre to slot home.
The Canaries went back in front after 25 minutes when Darel Russell laid the ball back for Holt to power home after an almighty scramble in the Stockport area.
And the hosts should have stretched their lead before the break with Chris Martin being denied at the back post by some superb, last-ditch defending from Paul Huntingdon.