Sutton, who moved to Wycombe last summer and scored six goals for the club, said he was looking forward to making his Motherwell debut and playing in the Uefa Cup.
"Europe is also massive for us," he said.
"As I understand it, if we win one tie we'll be in the group stages and could play against some massive clubs so I'm really looking forward to that.
"Motherwell, to a certain extent, were the surprise team last year and to finish third was a hell of an achievement. I want to come here, score goals, and help us get there again."
Sutton, who began his career with Tottenham before heading for Raith Rovers and Millwall, joined St Mirren from Dundee in 2005.
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