Mandaric, 73, almost quit the club following a backlash from fans when he sacked Megson and installed Dave Jones as manager in February with the club lying third in the table, two points behind Sheffield United, who had two games in hand.
Megson lost his job on the back of two wins from 10 games, but the Owls have not lost under Jones and 10 victories and three draws later the club have overhauled their city rivals to clinch automatic promotion following Saturday's home win over Wycombe.
When asked if he now felt vindicated by his decision to get rid of fans' favourite Megson, Mandaric said: "To be honest it's not so much that, I'm just so happy with this situation. I'm more concerned with what happens next. But we had no consistency. I did not want the play-offs.
"We all know where things are and what happened there and I don't want to go into all that again, but he has been a part of the season and I don't want to take anything away from him. But I had to do what I did. I sensed we were on a slippery slope and I had commitments. I had made promises.
"Some people were not with me at the time, but I did it for the good of the club. We did not have a team that looked like they would get promoted. Even if you go into the play-offs in good form it doesn't count for anything. I saw what was happening. I was upset at the reaction of some people, but we don't want to look back too much and of course he deserves credit for recruiting some very good players."