The English born attacker, who can also play as a winger, scored 12 times in 48 appearances for Maidstone between 2019 and 2021.
His arrival follows the recent departure of ’Well strikers Devante Cole and Chris Long.
Fir Park gaffer Graham Alexander is delighted to have secured Amaluzor – who trained with ’Well last season – on a one-year deal.
He told the club website: “Justin came in to train with us last season and immediately impressed us all with his enthusiasm and attacking ability. He’s hungry to succeed and we’re delighted to bring him in.
“We’re sure he’ll take this opportunity and be a valuable asset to our team.”
Motherwell will play a behind closed doors friendly against Dumbarton at The Rock this Saturday, kick-off 12 noon.
The Steelmen’s first competitive fixture of the 2021-22 campaign will be at Queen’s Park in the Premier Sports Cup on Wednesday, July 14, kick-off 7.45pm.
Further group games will follow at home to Queen of the South (Saturday, July 17, 3pm), at Airdrie (Tuesday, July 20, 7.45pm) and at home to Annan Athletic (Saturday, July 24, 3pm).
The new Scottish Premiership campaign starts at home to Hibs on Sunday, August 1, KO 4.30pm.