The German centre-half has agreed a three-year deal at Deepdale which will take effect on July 1 and moves on a Bosman.
Bauer, 26, turned down the offer of a new contract to make the move to North End.
He was Charlton's hero in the League One play-off final at Wembley last month, scoring their stoppage-time winner against Sunderland.
PNE manager Alex Neil is pleased to kick-off his summer recruitment with the capture of Bauer.
Neil said: "Patrick is a strong and powerful defender who we have monitored closely.
"He has experience of playing at the top level in Portugal and adapted very well to English football in the past few years.
"Patrick will add more competition to our defence and in the central positions."
Bauer started his career in Germany with Stuttgart, then moved to Portugal to play for Maritimo.
He joined Charlton in the summer of 2015 and his first season with The Addicks was in the Championship.
Bauer said: "I am really excited to be here and happy to play finally in the Championship again.
"I can’t wait to meet all my new team-mates, all the staff and management and get started.
"I was four years at Charlton, we had some disappointing moments, but also highs, like the promotion this season.
"I spent a good time there, but it was time for me to start a new chapter in my career and I am really excited to be here now."