The Latics boss is under no illusions that Stam can replace his fellow Dutchman, Mario Melchiot, at right back for the Latics. Martinez also believes Stam is capable of becoming a regular for his national side.
He told the club's official website: "We're extremely excited at Wigan Athletic to welcome Ronnie into our club.
"At 26 years of age he is at the peak of his career and, after playing a massive role in FC Twente's championship winning season last campaign, it is fantastic to bring a player of such calibre to our club.
"I'm sure the fans will welcome Ronnie and help him to enjoy his football here, whilst also becoming an important member of the Dutch national side."
Meanwhile Stam himself added: "It's really exciting for me to be joining the English Premier League, I can't wait to get started now!"