The Newcastle United midfielder was initially set to spend thee months with the Lions after arriving in early August but will now stay until the New Year.
24-year-old Northern Ireland international Ferguson will now make The Den his home until January 9.
NEWS | Shane Ferguson has extended his loan stay at #Millwall until January 9th 2016. #DeadlineDaypic.twitter.com/EeDF91KBgQ
— Millwall FC (@MillwallFC) September 1, 2015