The pair, who were both called up to Martin O’Neill’s Republic of Ireland squad for the first time last month, have agreed two-and-a-half year contracts at Deepdale and will join Preston on January 1 when the transfer window opens.
Boyle, 25, made over 150 appearances for Dundalk while Horgan, 24, scored 27 goals in 132 games – helping the Irish champions reach the final qualifying round of the Champions League before competing in the Europa League group stage.
Both players will require international clearance before they are eligible to play for their new club.
Preston manager Simon Grayson was delighted to see off competition for the duo’s signatures.
“First and foremost, we have signed two players who have attracted a lot of interest from a lot of clubs over the past few weeks and months and we have had to work hard to get them, which shows our intent as a football club,” he said.
“Both players have had great seasons in their league and in Europe, leading to their call-ups for the Irish squad. They are young, hungry and looking to improve and will be excellent acquisitions for us.
“They both have the desire to keep improving and joining a Championship club is the next progression for them – we have always tried to improve and we look forward to working with them.”
Boyle, who captained Dundalk during their Europa League fixtures, admitted the move was a fitting end to a memorable year.
“I can’t wait to get started,” he said. “Once I heard Preston were interested in me and I got over and had a look around it was the only place I wanted to come to. I knew of the history of the club and I am now really looking forward to getting going.
“We have had a great run with Dundalk in Europe and won the league and then I got the international call-up, so it has been a great year and this has capped it off.”
Horgan added: “It is a good team who like to try and play football, which was key for me. I met the manager and I was impressed by everything that he had to say, so that all helped massively, it just all seemed to fit and hopefully I can fit in here.”