She has won 58 international caps and was in the Portugal team that lost 2-1 to England at Euro 2017.
Villa boss Gemma Davies said: “We’re very excited about Diana. She’s a young, energetic forward who’s very technical and likes to drive at players 1v1″.
“We’ve picked up a young talent who’s been doing very well with her national team and scoring goals”.
“We’ve been monitoring her progress since before lockdown and we’re really excited that she’s finally an Aston Villa player.”
On completing her move to England Silva explained “I wanted to take a new step in my career and do something different.
“I want to be better as a player and as a person, and Villa seemed like a very good opportunity.
“I’ve never been out of Portugal, so it’s a big step for me. I achieved a couple of championships with Sporting and I hope to conquer more here.”
“I hope to score goals, to be happy here and to help Villa stay in the Super League as it’s the first season in the top league,” she said.
“It’s very encouraging [the signings Villa have made] and I think we will have a very good, very competitive team.
“I’m just super excited for the season to start and happy with the team I’m joining.”
The 25-year-old follows Birmingham City’s Chloe Arthur and Chelsea’s Anita Asante in moving to Villa, who won promotion to the WSL last season.