Barrera, who was a standout performer for his national team during this summer’s FIFA World Cup, has signed a four-year contract, with the option for a further year, in a £4 million deal.
The 23-year-old has completed his medical and finally signed on the dotted line on Friday morning once his work-permit has been approved.
Speaking to the official site for his first interview Barrera said, “I am very happy to sign for West Ham United and have been really taken by the reception I have received from the players and the manager, I have had a great welcome.
"I knew about West Ham when I was in Mexico. They are a big club and I have heard about the great players they have had in the past. I have heard a lot more about the club and its traditions since I have been in London and I am very excited to be here."