Ahmed Hegazi has signed a four-and-a-half-year deal with West Brom to turn his loan from Al Ahly into a permanent transfer.
Egypt international Hegazi has been ever-present for the Baggies in the Premier League this season, but has been unable to prevent their slide into the drop zone.
The defender scored on his debut to seal a 1-0 win over Bournemouth on the opening day of the season, but West Brom has not won since the fixture which followed – a 1-0 win at Burnley – leading to the departure of Tony Pulis as head-coach.
Replacement Alan Pardew is yet to oversee a win but Hegazi believes an upturn is around the corner.
"I am very happy with the club and very happy to be part of this group of players," he told the Baggies' official website.
"I know the results are not what we would want at the moment. But there is great spirit here and I am sure that we will turn the results in our favour before long."
West Brom sits in 19th place in the table following its 2-1 home defeat to Manchester United on Sunday.