The 26-year-old Londoner has refused to sign a new deal and revealed he is eager for a new challenge after playing a key role in the Swans' promotion to the Barclays Premier League.
Pratley made 179 appearances for the Welsh club and scored 27 goals, including a stunning strike in the npower Championship play-off semi-final second leg win over Nottingham Forest.
Swan song: Pratley's played his last game for Swansea
He told the club's official website: 'I'd like to thank the chairman (Huw Jenkins), manager and especially the fans for a wonderful five years.
'But after five years I feel the time is right for a fresh challenge. It's been a difficult decision for me and my family to make because Swansea is a fantastic club with such friendly and passionate supporters.
'It's not going to be easy for me, but if there was a good time to leave then it's now, with the club having secured their place in the Premier League.'
Out on a high: Pratley helped Swansea to promotion
?Bolton eye Celtic midfielder Kayal as Lennon ponders fresh move for McFaddenBolton reject Wigan bid for Al-Habsi is as Trotters want an increased offerCoyle set to launch fresh bid to lure Blues star Sturridge back to BoltonAll the latest Bolton news, features and opinion
?
Source: Daily Mail
Source: Daily Mail