The 18-year-old has put pen to paper on a long-term contract with the London club.
The Hammers’ technical director Tim Steidten spoke about the quality of the talented South American flier.
“We are really happy that Luis Guilherme is now a West Ham United player,” said Steidten, per club media.
“He is a very exciting young talent who we have followed for some time, and once we became aware that he was available, Julen and I were determined to bring him to London.
“Luis has enjoyed a fantastic start to his professional career with Palmeiras – naturally a wide player but with the flexibility to play across other attacking positions, which is an important and valuable factor in the modern game.
“He is technically very gifted, but also has very good physical qualities - great pace, strength and stamina, and these are traits that will help him to adapt to the demands of the Premier League and English football.
“Luis is obviously still very young, but we have no doubt that he is ready to make an impact in the first team here. He is coming to a great environment, where he will be surrounded by other exciting young players and good people who will support him every step of the way.
“We will look after him, help him and his family to settle in and allow him time to adapt. But we are very excited about his immediate potential and are looking forward to seeing the progress he can make at West Ham United.
“This is a very important signing for us – we’ve worked hard across the Club, working closely with the Board, to secure Luis’s signature. We know how the tough the Premier League is, and we want a squad that is competitive next season, but also to find the balance of ensuring that we plan for the longer-term future. Exciting young players like Luis Guilherme will help us to reach those goals.”