Browne, who has captained the Republic of Ireland Under-19s, caught the eye of North End boss Simon Grayson while playing with Cork City.
The 18-year-old was given a trial with the club and has impressed Grayson enough to win a deal at Deepdale.
"We became aware of Alan playing in Ireland, asked him over for a week's trial and liked what we saw," said Grayson.
"We think he has a bright future; he's got fantastic energy about him, is two-footed and is a goalscoring midfielder. He's still young, represents the Republic of Ireland and we feel he can improve over the next few months and years.
"He has different characteristics to the other young players we have at the club and we are trying to bring these players through, to develop them as professional football players.
"It worked in our favour that the Irish league finished in early November and we struck a deal that he could come and train with us for two months before he actually signed. He has been doing all the work they've done in the gym, yoga, on the fitness side and on the training ground and he's a very fit lad.
"He is grasping full-time training and that has been valuable for both of us. He has been able to get up to speed and get used to full-time training before the competitive football starts. He has played a couple of behind-closed-door games and there have been encouraging signs; so hopefully somewhere down the line he gets an opportunity and can show people what he is capable of doing."