The 27-year-old is reunited at the Britannia Stadium with Mark Hughes, who previously managed the midfielder at Manchester City and under whom the Irishman was awarded with City's Player of the Year award after their 2008-09 campaign.
The playmaker has since enjoyed spells at Aston Villa and, on loan, Newcastle United, but has been unable to find any real consistency in form and fitness since departing Eastlands in summer 2010.
The Potters' chief executive Tony Scholes welcomed the addition of Ireland, telling the club's official website: “Stephen is a player that Mark knows really well and when the opportunity arose he was keen to add him to his midfield and attacking options.
“Arguably the most successful period of Stephen’s career to date was when he played for Mark at Manchester City and we hope that he can rediscover that form.”
Stoke do not expect to wrap up any more deals before the summer transfer window closes, announcing via their official Twitter account that: "the Club do not anticipate making any further additions to the squad before the 11pm deadline".