Miandad, who was replaced with Bob Woolmer on Wednesday, said he had decided to quit after the Board refused to grant him powers relating to team selection.
"I had told them clearly to give me more authority and power. I had asked for a team of my choice. They said this was difficult so I told them to go ahead and do what is best for Pakistan cricket," the 47-year-old former captain said.
"I felt if I was not getting what I want to make the team improve its performance, it was no use to carry on like this. But we reached a mutual understanding that they will honour my remaining contractual terms and conditions and I will step down myself," he was quoted as saying in local daily The News on Thursday.
Miandad, who has now been sacked for the third time, said it was "unethical to announce Woolmer's appointment and my sacking in one breath. It is unfair that you have one person under contract and bargain with another for the same post. They should have taken me into confidence and announced Woolmer's appointment after two or three days."
Had he known the Board was going to give the impression that it had sacked him, he would have announced his stepping down himself, he said.