Midfielder Evans joins Gary Bowyer's side on a three-year deal, having been at the KC Stadium for two-and-a-half years after arriving from Manchester United.
Meanwhile, Cairney, 22, heads to Ewood Park on loan until January 2014, with manager Bowyer suggesting the Scotland under-21 international could feature in their Championship opener against Derby County on Sunday.
"I'm delighted to get him," he told the club's official website.
"We have to thank Steve Bruce and Hull City for allowing him to come here on loan.
"He's a talented technical player, someone who can dominate midfield and pass the ball. It has been no secret that we've been after one this season.
"He's got a great left for his deliveries from set-plays and he's a great lad, I just spent a couple of hours with him today and he's the right character for the dressing room."
Evans is Blackburn's third signing in two days after Tommy Spurr made the switch from Doncaster Rovers.