The Hammers have sealed a deal for the 21-year-old to join the club this month on an 18-month loan without an option to buy.
West Ham boss David Moyes wants to add a midfielder to his squad, and Fernandes is expected to complete a move in the coming days.
The likes of Everton, Chelsea and Manchester United have all been linked with the Portugal under-21 international, but it appears the London Stadium outfit have beaten fierce competition to land their man.
Fernandes have already fallen out with manager Bruno Lage at Benfica and haven’t featured in their last seven matches, making a January exit certain.
West Ham could do with another quality midfielder in their ranks given their lack of quality depth in the department, and the youngster would be a fine addition given his massive potential.
Fernandes wants to move to London as his mum lives there, while he also has friends from Portugal in the Hammers youth teams, and the feel-at-home factor should play a huge role in ensuring he settles down quick and hit the ground running.