The 21-year-old was unveiled by the east London club on Thursday. He has represented Portugal at every level from U15 to U20. Silva will join the club's U23 team for this season.
Speaking at his unveiling, Silva said: "This is a very important moment for me. This is a new experience for me, out of Portugal. I am very happy to be here at West Ham," the player told the club's official website upon his unveiling.
"I am a technical player and I am very fast. I will give West Ham 100 per cent on the pitch every time I play.
"It's a big dream of mine to play here in England."
A new face at The Academy of Football... #WelcomeXandepic.twitter.com/yZkj52MzNj
— West Ham United (@WestHamUtd) August 2, 2018