Southend have agreed to cancel Steve Mildenhall's contract by mutual consent to allow the goalkeeper to join Millwall on a one-year contract.
The 32-year-old, who joined the Shrimpers in the summer of 2008, had previously revealed a desire to leave the club in order to play his football at the highest possible level.
Mildenhall will now get his chance in the Championship with Millwall following an announcement from Southend.
A statement on Southend's official website read: "The club's management wishes Steve all the best for the future and thanks him for his service over the past two seasons."
Millwall begin their 2010/11 Championship campaign away to Bristol City on 7th August.