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."