The outstanding Portugal international centre-half joins the Hammers from Southampton on a two-and-half-year contract with the option to sign for another season for a fee of £8million.
Fonte was linked with a range of clubs in the top flight before opting to move to London Stadium
The experienced central defender has enjoyed a successful career in English football since initially joining Crystal Palace in 2007, before going on to make 154 Premier League appearances and captain Southampton for the past three-and-a-half seasons.
A strong and technically-gifted defender and respected leader, Fonte wants to take his career to another level at London Stadium and revealed that he cannot wait to pull on a Claret and Blue shirt for the first time.
Fonte said: “I signed for West Ham because they are a great club and a very big club. They have a lot of fans and I have known for a number of years how passionate they are.
“The manager was also a very big influence. I thought that he really wanted me and that he sold me the project and the ambition of the Club.
“I also have part of my family living in London and they are big West Ham fans. It just made sense for me at this stage to join West Ham. It is a new challenge and a new beginning and I am looking forward to it.
“With the way that West Ham is going we can only look to be challenging in the top eight.
“I told the manager in conversations that we want to win and we want to win trophies. The ambition is big and we need to aim high.
“West Ham are a massive club and it is an exciting challenge and it should be for everyone. We all need to get together and start working.”
I signed for West Ham because they are a great club and a very big club. They have a lot of fans and I have known for a number of years how passionate they are.
Fonte began his career in Portugal where he spent a decade at Sporting B and eventually caught the eye of Lisbon’s other giant, Benfica.
A move to the Estadio da Luz followed in 2006, but with first-team opportunities limited, he moved to England in the summer of 2007 and signed for Crystal Palace, where he made 92 appearances over three seasons.
In January 2010, Southampton manager Alan Pardew moved for Fonte, and he was part of the team that won the Football League Trophy at Wembley just a few weeks later – featuring alongside a certain Michail Antonio.
As the Saints marched to a second consecutive promotion – narrowly beating the Hammers to second place in the Championship – Fonte’s own reputation grew as he seamlessly settled into life at a higher level.
That trend continued as Southampton established themselves in the Premier League from 2012 onwards, with their Portuguese defender a virtual ever-present under managers Nigel Adkins, Mauricio Pochettino and Ronald Koeman.
After being appointed captain in summer 2014, Fonte won his second Player of the Year award at the end of a season that also included his senior international debut in a friendly win over Argentina in Manchester.
Since then, he has been a regular member of the Portugal squad, and forced his way into the starting XI for the knockout stages of UEFA Euro 2016.
There, he played every minute as the Portuguese defeated Croatia, Poland, Wales and France to achieve a historic success.
Fonte will not be available for Saturday’s Premier League fixture at Middlesbrough, but could make his West Ham debut at London Stadium when Manchester City visit on Wednesday 1 February.