It has now been confirmed that Wilder will try to move the club from their position at the bottom of the League Two table.
Northampton chairman David Cardoza said: "I am delighted to be able to appoint Chris. I know it has been a frustrating time for our supporters and I apologise for that but I make no apologies for taking our time and making sure we made the right appointment.
"We were in the capable hands of Andy King so we took our time, assessed our options, spoke to a lot of people in the game and all the reports we got on Chris were excellent.
"We were looking for a manager who has the experience required to guide us out of our current position and one who is ambitious and driven enough to take the club forward in the medium term and Chris is the perfect choice."
Wilder spent just over five years at Oxford.