North End made a couple of attempts to sign the youngster from Oxford in January but were quoted with a figure of £1 million which Preston were not prepared to meet.
Ledson agreed to stay at Oxford for the remainder of the season knowing that with one year remaining on his contract Oxford would be forced to cash in on the midfielder.
The youngster will provide competition for places in midfield especially alongside Ben Pearson. In reality he has replaced the outgoing Welsh and is a sign that Preston are seeking to improve their squad with young hungry players.
The fee was undisclosed but Ledson will be hoping to make an immediate impact with Preston who will be attempting to improve upon last season's seventh place finish.