In an open letter to Villa's supporters published in the Birmingham Mail on Wednesday, Barry said: "I want the chance to explain my decision.
"I have a massive fear of going stale and falling into a comfort zone.
"After changing my mind lots of times I came to the decision that the time was right for me and the club to part.
"I have grown bored of all the speculation surrounding me over the last 12 months and I am sure all the fans have as well.
"I am glad I never left last summer because I would have left under a cloud. This year I feel things are different."
Barry moved to Villa from Brighton as a 16-year-old in 1997 and played over 400 games for the Birmingham club, as well as winning 29 caps for England.
"I feel the club is in the best position it has been in during my time here," added Barry.
"We have very good young players, a fantastic chairman and one of the best managers in the game.
"I want to thank them [the Villa fans] for the incredible support I have received over the last 12 years.
"For the rest of my life Aston Villa will be the first result I look for. Thanks for everything."