Ireland, 27, follows Austrian international forward Marko Arnautovic to the Britannia Stadium after he completed his move from Werder Bremen.
Stoke boss Mark Hughes managed Ireland at Manchester City and the club's chief executive Tony Scholes hopes the midfielder can recapture the form he showed then.
Scholes said: "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."
Arnautovic, 24, has signed on a four-year contract from Werder Bremen and joins other new signings of Erik Pieters, Marc Muniesa and Oussama Assaidi.
The club said on their official Facebook page: "Stoke City are delighted to sign Austria international winger Marko Arnautovic from German side Werder Bremen.
"He joins on a four-year deal for an undisclosed fee."
The move for Arnautovic, who had a brief and troubled spell playing under Jose Mourinho when he was manager of Inter Milan, was reported to be worth around £2million.
Arnautovic follows Holland defender Pieters, Spanish centre-back Muniesa and Liverpool loanee Assaidi at the Britannia.
Source: PA
Source: PA