As per the reports, Fredericks has signed a four year deal with the Hammers.
The former Spurs defender helped Fulham secure promotion to the Premier League but he will not play for them next season.
At one point, it seemed like the defender would sign an extension with the Cottagers but the two parties struggled to agree on a new deal and Fredericks will now look to continue his career with West Ham.
The 25-year-old wanted to become Fulham’s highest earner with wages of around £40,000 per week.
Fredericks will add some much-needed depth to West Ham’s full-back positions. The likes of Zabaleta and Byram have struggled to impress so far and the Fulham star could secure a starting berth for the Hammers if he performs well enough.
The 25-year-old will be Manuel Pellegrini’s first signing as the West Ham manager and the transfer will be officially confirmed next week.