The Czech Republic international penned a four-year deal with the club and expressed his delight at fulfilling a dream move to the Premier League
The 24-year-old, who was top goalscorer in the Europa League last season with 10 goals, has signed a four-year contract with the Midlands club to become Paul Lambert's seventh signing of the summer.
Lambert admitted the club had been trailing the player over the summer having been impressed with his record in Europe last season, and now wants him to provide cover for star striker Christian Benteke.
"We've been on this one for the last few months, trying to bring him to the club, so I'm delighted to get it across the line," Paul Lambert told the club’s official website.
"Libor has an unbelievable scoring record in the Europa League, incredible really. He wasn't given much opportunity for Lazio in Serie A.
"But he showed proper potential in leading the line there at a strong club with a great tradition and we need somebody like him as we only have Christian Benteke really as a main target man.
"Libor's powerful, too, and I'm looking forward to working with him. We needed to bring in someone like Libor to help the overall philosophy to work."
The giant striker, who stands at 6ft 4 inches, expressed his delight at becoming part of Lambert’s new-look side and revealed the move is helping him realise a dream in moving to the Premier League.
"I hope it's a good step for me and also for Villa because everything is about the team," he enthused. This is a big club, a very historic club with a fantastic fanbase and, for me, this is really important.
"From when I was a young boy, I have dreamt of playing in the Premier League and to do this with a club such as Villa is incredibly motivating. It's real now and I'm very happy about this.
"I scored goals in the Europa League last season and I'm happy about this because it's not easy but I know it won't be easy either to score goals in the Premier League so all my focus will be on this now."