The 29-year-old becomes the Whites’ seventh summer addition, providing further attacking strength and experience for Steven Schumacher’s squad.
Hardie will reunite with Schumacher, his former manager at Plymouth Argyle, ahead of Bolton’s Championship opener against Preston North End on Saturday.
Hardie was Argyle’s top scorer during their title-winning campaign and later twice reached double figures in the Championship. He will now look to make another strong impact at Bolton.
“It’s a massive factor. I can't beat about it,” said Hardie.
“He was one of the reasons I went to Plymouth and one of the reasons why I did so well there.
“We've had promotions together and we've done well in the Championship at parts before he left. So, yeah, he's a massive part in it and I'm looking forward to working with him again.”