Benrahma joins the Hammers on an initial £4m loan which will become a permanent £25m switch next year.
A further £5m in clauses could follow, which would make it the £30m (€33m) operation first reported.
He will wear the number 9 shirt at West Ham.
We are pleased to announce the signing of Algeria international Saïd Benrahma on loan from Brentford ✍️⚒#WelcomeSaid
— West Ham United (@WestHam) October 16, 2020
The Hammers were in advanced talks with Brentford at the weekend for 25-year-old Benrahma, but the deal almost collapsed today.
Citing concerns from the second part of Benrahma’s medical, West Ham moved to renegotiate the terms of the transfer.
Instead of an outright sale, West Ham asked Brentford for a loan with an obligation to buy.
Brentford finally agreed to the request, meaning Benrahma will now play Premier League football for the first time.
Last season the talented winger scored 17 goals and contributed 10 assists in the Championship.
“I’m very, very happy to be a part of this team,” said Benrahma in his first interview. “West Ham is a historic club, which has been in the Premier League for a very long time. It included and still includes good players. It’s a massive club in England.
“I spoke to the manager, so I know exactly what he expects from me. I’ll try to meet his expectations on the pitch because he’s put faith in me and hopefully I can give it back on the pitch.
“I like this prospect [of playing in the Premier League]! I play football to enjoy myself first and foremost, but it’s always enjoyable to know you’re joining the most-watched league in the world, so I’m definitely looking forward to showing what I can do.”