"I am absolutely delighted to join. I am over the moon. It's taken a while but now it's done I am excited and looking forward to meeting my new team-mates and getting on the pitch and playing football," the 25 year old told the club's website.
"There's been a lot of speculation and rumour about the deal and it has played on my mind a little but I've been professional and kept my head down."
Sidwell endured a frustrating time at Chelsea last season after joining on a free from Reading.
"I am here now and can't wait to put a Villa shirt on and play for the fans. For me personally, it's about getting back and playing," he said.
"I have had a year of not playing as much as I would have liked so to get out on the pitch is the first aim.
"It's straight down to work really. I have already done some pre-season with Chelsea but the hard work starts now.
"I can't wait to get out on the training field and meet my new team-mates. I have heard they are a good bunch of lads.
"I am sure I will settle in fine and I'm sure the players will be fine with me."