ALBION boosted their midfield options by signing the Argentina international in July.
The holding midfielder penned a three-year contract, plus a year’s option in the club’s favour, after passing a Hawthorns medical.
Yacob, who was a free agent after leaving Argentine Primera Division outfit Racing Club de Avellaneda at the end of last season, will wear his now customary No.5 shirt with the Baggies.
The 25-year-old became Albion’s third summer recruit, following England international Ben Foster and season-long loan signing Yassine El Ghanassy into the club.
Yacob started his career at Racing, where he has spent the last six years, becoming an influential figure and captaining them since 2008.
The 5ft11in ace is renowned for his tenacious performances and passing ability and has two senior caps to his name, having scored on his last appearance – a 2-2 friendly draw with Ecuador in April 2011.
Yacob was also part of his country’s Under-20s team that won the 2007 FIFA World Youth Championships in Canada, making 20 appearances at that level in total.