Horgan, 26, joins 'Hibs' for an undisclosed fee.
The midfielder won three league titles in a row at Irish side Dundalk before moving to Preston in January 2017.
Manager Neil Lennon reacted to the signing: "He's one we've been keen on for a long time and it's a real coup to get him over the line.
"Daryl will give us a real threat going forward and some strength out wide - we had been looking to add in that area and I'm delighted with the options we now have.
"He has power and pace and will hopefully give us another dimension to our play in the final third."
Horgan was pleased to make the move: "I've spoken to the manager and am excited for his plans for the season ahead.
"Obviously the boys have started well in Europe and the league - they had a good season last year and the ambition is there to follow that up with another successful year.
"I'm ready to play and looking forward to trying to break into the team.