The 26-year-old has been at Ewood Park since 2011 and made 106 appearances, scoring seven goals.
Dann has now completed his move to Palace, signing a three-and-a-half year deal with the south Londoners.
The Eagles announced the centre-back's arrival on Twitter, while Blackburn released a statement shedding light on the terms of the deal.
"Rovers defender Scott Dann has this evening completed a deadline-day move to Crystal Palace," read the statement on www.rovers.co.uk.
"The 26-year-old joins the Barclays Premier League club for an undisclosed fee, signing a three-and-a-half-year deal."
Dann becomes Palace's third signing of deadline day, following moves for Wolves goalkeeper Wayne Hennessey and Jason Puncheon, whose loan from Southampton was made permanent.
Blackpool's Tom Ince and Celtic midfielder Joe Ledley are still on Palace's radar, while Nurnberg have signed Jose Campana on loan with a view to a permanent move.
The Eagles have yet to officially confirm that deal, but did announce the mutual termination of Wales defender Darcy Blake's contract.
Source : PA