Keegan says he felt vindicated after a tribunal awarded him £2million in damages from Newcastle for his constructive dismissal from the club last year.
Newcastle, on the other hand, refused to make a comment on the matter after learning the outcome.
Keegan: "I took the decision to resign in September 2008 only after very careful and anxious consideration.
"The decision to resign was one of the most difficult decisions that I have ever had to take in my life.
"I believe that anybody who knows me and my attachment to Newcastle United and the north-east in general will understand how difficult this must have been.
"I very much hope that the decision of the tribunal now confirms why I felt that I had no option but to resign from the position as manager of the club that I love.
"The tribunal has found the conduct of the club in forcing a player on me against my wishes represented a fundamental breach of my contract of employment.
"I do not believe that there is any manager in football who could have remained at the club in the light of their conduct.
"I resigned because I was being asked to sanction the signing of a player in order to 'do a favour' for two South American agents.
"No-one at the club had seen this player play and I was asked to sign him on the basis of some clips on YouTube.
"This is something that I was not prepared to be associated with in any way.
"The club knew that I objected strongly to this transfer and were aware that by continuing with it, I was likely to feel that I had no option but to resign.
"Notwithstanding this, they nevertheless went on to sign the player at very substantial cost to the club."
The panel, which comprised Philip Havers QC, Lord Pannick QC and Kenneth Merrett, said: "We declare that Kevin Keegan was constructively dismissed by Newcastle United Football Club Ltd, for which Newcastle United Football Club Ltd must pay to Kevin Keegan damages in the sum of £2million plus interest to be assessed if not agreed."