ALBION completed their second summer signing of 2012 by snapping up the Belgium international.
The 22-year-old AA Gent winger joined the Baggies on a season-long loan deal - subject to international clearance and Albion have an option to make the move permanent.
El Ghanassy, who can play on either flank and also as a striker, has passed a Hawthorns medical and will wear the No.10 shirt.
He has become renowned in Belgium for his pace and trickery on the ball and won the first of his two full international caps against Finland in February 2011.
Head coach Steve Clarke said: "I'm delighted to welcome Yassine to the club.
"He is an exciting, young prospect who will hopefully add something different to our squad.
"This is a big move for Yassine and we'll have to be patient with him as he settles into a new country and gets to grips with the demands of the Barclays Premier League.
"But we believe he has got the raw talent to make an impact here."
El Ghanassy made 37 appearances for AA Gent last term, scoring seven times, as they finished third in the Belgian top flight.
In 2010, he helped the Buffalos complete the double - winning the Belgian First Division and Belgian Cup in the same season.
The 5ft9in player joined AA Gent from Third Division side La Louviere in 2008 and has played in both the Champions League and Europa League during his four years at the club.
Sporting & technical director Dan Ashworth said: "Yassine is a player we have watched develop for a couple of years.
"He has shown in Belgium his ability to put defenders on the back foot and create and score goals and he is on the fringes of the national team.
"He is an exciting, young player who we hope will grow into the league and prove a real asset.
"He offers us a different option and is the type of player I am sure our supporters will warm to and get right behind."
El Ghanassy's international career began with Belgium under-19s and he has six under-21 caps to his name, scoring once.
In total, El Ghanassy has made 147 appearances in all competitions for AA Gent, scoring 17 goals.