The defender moved to The Den on a two-year deal with the option of an additional 12 months.
Hutchinson, 25, began his career with Motherwell, making his debut in 2009, and featured a further 140 times. During his time with the Scottish club he picked up experience of playing in the Europa League and Champions League qualification stages.
The centre-back, who was born in Newcastle, joined West London side Fulham in 2014, making 31 appearances in his first season at Craven Cottage. His opportunities were more limited in 2015/16, though, when he featured 11 times, prompting his decision to depart and join Millwall.
Hutchinson will wear the club’s number four shirt in 2016/17 and is set to compete with Byron Webster, Tony Craig and Sid Nelson for a starting berth at the heart of the defence.