The 35-year-old was a free agent after being released by Stoke in the summer and becomes new manager, Kenny Jackett’s first signing since taking over the Championship’s bottom club on 21 October, replacing Alan Stubbs.
The deal however is subject to the English FA and EFL ratification.
“Class is permanent, form is temporary, so I just need to find my form. All the movements are still there,” the former West Bromwich Albion striker said.
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“Rotherham and Bolton showed interest over the weekend. Time is not on my side at my age and the Championship is a bit closer to where I wish to be.
“Thanks to Bolton for their interest in me but I’m really pleased to join Rotherham. Kenny showed some interest in me a few months ago and we have been in touch since then. I am pleased he got a job and he offered me a contract.”
Odemwingie last played a competitive match on 19 April, 2016.