The sides were level at half-time with Alex King kicking two penalties and Saints replying with a Carlos Spencer drop goal and a Bruce Reihana penalty.
Wasps looked liked they had sealed victory when Reddan crossed and King added another three points.
Saints did get some hope when Rhodri Davies went over but Hoadley's late try sealed victory for Wasps.
Northampton coach Budge Pountney:
"It is infuriating that we are creating chances and can't manage to finish them off. "We were just making a few bad decisions while Wasps didn't have to work that hard to find the gaps when they scored."
Northampton: Reihana (capt); Diggin, Clarke, Quinlan, Rudd; Spencer, Robinson; Budgen, Richmond, Barnard; D Browne, Gerard; Fox,
Harding, D Browne.
Replacements: Vilk for Diggin (45), Davies for Rudd (55), Howard for Robinson (77), Harbut for Budgen (67),
Hartley for Richmond (72), Lord for Gerard (41), Lewitt for D Browne (70).
Wasps: Voyce; Sackey, Erinle, Abbott, Hoadley; King, Reddan;
Payne, Ward, Bracken; Skivington, R Birkett; Hart, Rees, Lock.
Replacements: Baxter for Erinle (72), Staunton for Abbott (80),
Gotting for Ward (65), Mackenzie for Bracken (46), Shaw for R. Birkett (46), Dallaglio for Lock (46).
Not Used: Fury.
Sin Bin: Hoadley (27).
Att: 13,585
Ref: R Debney (RFU).