Miller came through the youth system at Manchester City before making a name for himself at West Bromwich Albion, but the striker soon found himself failing to settle at a number of clubs in the EFL.
The 31-year-old has been without a club for more than a year after last representing Bury in League One, but Oldham have now opted to hand the player a 12-month deal after a successful trial period.
Miller told the club's official website: "It's been good to get pre-season under my belt and it feels good to be back in the game.
"It was just the perfect time for me to come back, I've been really missing them games. Especially the last couple months, things like the World Cup make you miss it so much.
"That year out it was nice to reflect on the things that I wanted and probably made me hungrier than I've ever been."
Miller could feature when Oldham begin their League Two campaign against MK Dons on Saturday.