The 26-year-old made 199 appearances during a five-year spell with the Swans, his last being in the npower Championship Play-off final win over Reading at Wembley which secured promotion to the Barclays Premier League.
Free transfer: Darren Pratley (left) arrives from Swansea City
'We're delighted to have Darren here,' Wanderers manager Owen Coyle said.
'A number clubs were interested in him and we are pleased to have secured his services.'
'He's an exciting player, who has the right characterto blend into our squad. He is a good addition as we look to progress our clubfurther in the upcoming season.'
Pratley becomes the second of the Swansea's play-off winning side to depart on a free after goalkeeper Dorus de Vries opted to move to Wolves.
And the former Fulham midfielder admitted the decision to move to the Reebok Stadium was the biggest of his career.
Big decision: Pratley jumps ship despite Swansea's promotion
'It was nice to leave Swansea on a high after gaining promotion to the Premier League and I'm now looking forward to showing the fans what I can do here,' the 26-year-old said.
'It was the biggest decision of my footballing career so far to leave Swansea.
'I enjoyed playing and living there and the club have been extremely good to me.
'It was always going to be a big decision for me regardless of whether Swansea got promoted or not.
'What's important to me is that I join Bolton as a Premier League player after that play-off final.
Looking to the future: Pratley can't wait to get started at Bolton
'I was delighted to have gained promotion with Swansea. I leave there wishing them well and I'd like to thank everyone there for supporting me.
'Now I'm really looking forward to Monday and getting into training and meeting the lads.
'The manager outlined some exciting plans and we had a good chat. I'm fully focused on playing well for Bolton.
'The fans can expect someone who always gives 100%.
'I like to get around the pitch and am a bit of a box-to-box player and hopefully I can chip in with a few goals.
'I managed to get 12 in my last season with Swansea. Hopefully I can continue to score goals from midfield at Bolton.'
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