Ireland joined Villa as part of the deal that saw former Leeds United player Milner move to big-spending City, with the 23-year-old believing he was not given a fair chance under manager Roberto Mancini.
He said: "I did feel unwanted at Manchester City.
"I was banging my head against a brick wall despite what I had done in training.
"I just went with the reserves, worked hard in the gym and kept as active as possible.
"Without a shadow of doubt the situation I found myself in will happen a lot at Manchester City with all the high-profile players they have at the club.
"At Manchester City sitting on the bench I didn't feel part of the team. I was neither happy or sad if we lost. I'm still young and hopefully Villa will get the best of me and I am now looking forward to the season."
The Republic of Ireland player, who is set to make his Villa debut against Newcastle tomorrow, his 24th birthday, has also warned Milner he may have to get used to not being a certain starter with City.
Mancini has a host of world-class players to call on and Ireland said of Milner: "I can see why he wanted to go to Manchester City.
"He can see the attraction of the move and the opportunity to become more established and become a superstar.
"But he faces a challenge of holding down a regular first-team place.
"I may have been forced out but I couldn't be more happy to be at Aston Villa.
"Richard Dunne is a good example of what can happen after leaving Manchester City to join Villa. A year on I can see how happy he is at Villa and I'm hoping that I will be as happy in a year's time.
"Richard was a huge part of Manchester City and it was a great shock to see him leave.
"It was as big a shock to him as everyone else but he could not have come to a better club as he proved with his performances last season.
"For me this is a positive, as this is exactly how I want it to be."
Villa's caretaker manager Kevin MacDonald is delighted to have Ireland on board.
MacDonald knows the attributes of Ireland as well as anyone, having coached him when he was the assistant to the then Republic of Ireland manager Steve Staunton.
MacDonald, who is still refusing to be drawn on whether he wants to succeed Martin O'Neill on a permanent basis in the Villa Park job, said: "Stephen Ireland is a very talented player.
"He is different from James Milner who is a power player.
"James has the drive to break the game up. He probably doesn't get into the box as much as Stephen Ireland. I think he glides across the pitch.
"I remember the first time I saw him training with the Republic of Ireland.
"I just thought I hadn't seen the kid before. He glides past people and rides tackles easily.
"His awareness of where his team-mates are on the pitch is fantastic and his choice on the weight of pass is one of his real plusses."
As for his own future, MacDonald added: "It's been nice so far but I am a reasonably intelligent man that I would know whether to accept or decline the job.
"I have no problem with the timescale as Mr Lerner (Villa's owner Randy Lerner) will be looking seriously at what he wants to do."
While Ireland has reservations about Milner making an immediate impact at Manchester City, his erstwhile team-mate Joe Hart has no such misgivings about another newcomer Mario Balotelli, who the goalkeeper believes will give City an extra edge up front.
Balotelli, 20, marked his debut by scoring the winner in the 1-0 victory against Timisoara in the Europa League play-off first leg match on Thursday after stepping off the bench.
The goal – a deft finish from close range – puts City firmly in the driving seat for the group stages with the return game at Eastlands next Thursday.
Balotelli's UEFA registration was only confirmed the day before the match following his arrival from Inter Milan.
Even though he has been at the club only a matter of days, Hart has already been tested in training.
Hart, now City and England No 1, said: "He has a great touch and a hell of a right foot, which is interesting to train against.
"He certainly announced himself. He had a couple of chances but it was good for him to get that first goal out of the way."
Balotelli limped off near the end and manager Mancini will monitor his fitness ahead of the home match against Liverpool on Monday.
Mancini said: "We do not think it is serious. It was probably just a kick, it is not a problem."
City improved in the second half after a slow start with Yaya Toure rattling the post before Balotelli scored an important away goal.
While Hart and the rest of the group returned home following the match, Shay Given, the man Hart has replaced in the first two games, was heading to Munich on his own.
Given was seeing a specialist in Germany after leaving Timisoara on an early morning flight.
The Republic of Ireland international told City fans at the airport he was having further treatment on his shoulder. He needed an operation after dislocating it in April in the 0-0 draw against Arsenal.
City have kept two clean sheets under Hart going into the match against Liverpool following the draw with Tottenham last weekend.
Mancini said: "Touch wood this will continue in the next game. It is important. We need time to improve and time to play together."
Milner is set to make his debut against Roy Hodgson's side after completing his protracted move from Aston Villa on the eve of the Europa League match.
Milner is the club's sixth high-profile signing of the summer as they attempt to clinch a place in the Champions League.
Jerome Boateng, Aleksander Kolarov, David Silva, Yaya Toure and Balotelli have all joined the City revolution.
However Boateng (knee) and Kolarov (ankle) are again ruled out through injury after sitting out the match in Romania.