Planet Swans ArchivesWilliams signed a loan deal with just minutes to spare of the transfer window and will go straight into the squad to face Hartlepool on Saturday.
It is believed that the Swans beat of competition from Cardiff City for the deal as well as rumoured interest from Leeds United.
The former Stockport player made his Wales debut last night and is expected to make his move permanent in the summer.
"I'm delighted to be able to sign a player with such potential as Ashley,'' explained Swans boss Roberto Martinez. "It's huge bonus that he is a Wel;sh centre-half with international recognition.
"With Kevin Amankwaah picking up an injury in the reserves this week and Garry Monk and Marcos Painter already out, it was imperative that we gave our players extra competition and cover until the end of the season.'
