Defender signs in
Lafferty, who has made ten appearances for Northern Ireland, started his career in the youth set-up at Glasgow Celtic and arrived at Turf Moor via Ayr United and his hometown club Derry City.
Lafferty told the Millers' official website: "I travelled with Burnley to Liverpool for preparation for the game last night then I got the phone call and spoke to Sean Dyche the manager and he confirmed the move. It all moved quite quickly and by the middle of yesterday I knew I was coming here and it was all done and dusted."
Lafferty will be in contention when the Millers take on Huddersfield Town on Saturday.