Mackay, who remains under investigation by the Football Association for an alleged text scandal during his time at Cardiff City, spent less than five months at the DW Stadium.
"You have to have a succession plan," Sharpe said in this morning's press conference. "Malky was getting results and we thought we'd turned it around when we won four games away in a row. We had another dip recently and we're now eight points behind with five games to go, we had to change it.
"I think it will be a seamless transition with Gary. For the club to get it's identity back I felt this had to happen. We like a certain style of football here and that's what we're looking to bring back."
Caldwell has insisted that he will implement his "own style" in his first managerial role.