Sheffield Wednesday and Millwall have agreed an undisclosed fee for the transfer of Mark Beevers when the January transfer window opens.
The defender initially joined the Lions on loan from Hillsborough in October and has since made 11 appearances for the Londoners.
Beevers came through the academy ranks with Wednesday, going on to appear 161 times.
The 23-year-old has agreed personal terms at the New Den and will join Millwall permanently on 1 January 2013.