Eagen has previously played for the Blades Inna loan spell from Sunderland in 2012. He played once during Danny Wilson's tenure.
He has completed a move from fellow Championship side Brentford, breaking the previous transfer record of £4m which brought James Beattie to the Lane from Everton in 2007. The former Gillingham defender has signed a 4 year deal.
Amid rumours that Brighton could sign James O'Connell, we only hope that Egan hadn't arrived as a replacement.