The 18-year-old striker says the Hammers' progress this season and the thought of playing in front of 60,000 people next season persuaded him.
It is a deal which has been widely reported in various stages in recent months, but West Ham United confirmed on their official website on Friday that they have finally secured the signing of Valencia prodigy Toni Martinez.
The 18-year-old striker is regarded as one of Spain's hottest teenage talents after scoring more than 100 goals at various youth levels for Los Che over the past four years, and also winning the 2015 European Championship with the Spain Under-19s side.
The Hammers revealed the teenage striker has signed a three-year deal effective from July but had been given permission by his club to train with his new teammates in England for the remainder of the season.
Martinez compares himself to former Liverpool and Chelsea striker Fernando Torrres, and admits that he had been persuaded to make the move so early in his career because of the progress West Ham have made on and off the pitch.
Speaking to the club's website, he said: "For me, it’s a great opportunity to be here and I hope to make the most of being at such a big club. I joined West Ham because of the progress that the club is making.
"The decision to come here was made because it is a brilliant opportunity to join an interesting club in the Premier League. The Premier League is well considered across the world and in Spain, we believe that it is one of the best leagues in the world.
"This is a fantastic opportunity and I am fulfilling a lifelong dream by signing for one of the big clubs in the Premier League. The prospect of playing in front of 60,000 people next year really catches my attention, and it is a Stadium that has so much history. I am hoping to be able to get the opportunity to do that and I hope that it will be soon."
With nearly four months to integrate himself at West Ham before the start of next season, Martinez will be pushing to be involved from the off when the Hammers kick off their first campaign in their new Olympic Stadium home in August.
The Hammers may yet have European football to play in that historic season, with the club sitting just three points behind Manchester United in fifth and five points off a first ever spot in the Champions League.