Uruguay International joins on loan
Martinez can play in defence or midfield and is a set piece specialist.
He joins the club on loan until the end of the season with a view to earning a permanent move in the summer.
The Defensor captain was recommended to Albion by former Juventus and Uruguay striker Daniel Fonseca.
Martinez said of the move, 'Everything happened so fast that I even didn't have the chance to visit my team from Defensor Sporting.
'The officials of Defensor and my agent told me that I had to gather my personal things as quick as possible because I have to travel to England and present myself in West Bromwich Albion.
'I am very glad of this chance and I hope that I can get adapted as soon as possible, most of all the weather because lately in Uruguay it has been very hot and I know that currently in Europe it's being very cold.'
Good luck Williams