The 25-year-old follows former Staggies team-mate Paul Lawson to Fir Park after agreeing a two-year deal.
Vigurs said: "I am absolutely delighted to be joining - Motherwell are a massive club who did so well last season.
"The club has a good fan base and a good manager in Stuart McCall. He was a big pull in me coming here and I am excited about working with him.
"Motherwell as a whole has a good reputation, I have heard nothing but good things and I just can't wait to get the season started now.
Motherwell chief executive Leeann Dempster admits she is happy with the rebuilding plans, as manager Stuart McCall prepares for next season.
Dempster said: "We are delighted we have managed to recruit both Iain and Paul for next season.
"Obviously this is a summer of change at Fir Park but with that comes a lot of excitement and Iain's signing typifies the calibre of player we are looking to bring in for our European and domestic campaign.
"In partnership with the manager, we are working through a list of targets and we are hoping to announce more new signings soon."