The 26-year-old joins the Premier League club from Al Ahly for the 2017-18 campaign with the option to make the move permanent.
The centre-back has already travelled to Hong Kong to link up with the squad for pre-season duties in the Premier League Asia Trophy.
“We’re pleased he’s here, he’s a good addition,” West Brom boss Tony Pulis told the club’s website. “He’s got good pedigree and has played for some good clubs. Hopefully he’ll be a good signing for us.
“With it being a loan and, if he does well, we’ve already agreed a final deal. It’s really, really good for us.”
Chairman John Williams added: “We’re delighted to add Ahmed to the squad.
“He caught our eye at the African championships and we’ve been tracking him ever since.”
The former Fiorentina man was part of the Egypt side that reached the Africa Cup of Nations final this year, which they lost to Cameroon.