New boy Palmer "ticks all the boxes" for Millers
The 22-year-old is Paul Warne's second January signing and has penned a two-and-a-half year deal.
Palmer boasts Championship experience on his CV after playing a major role last season in helping the Brewers maintain their second-tier status.
The Derby-born playmaker has made 14 appearances this term.
Millers chief Paul Warne said: "He's young, athletic and he can play. He ticks all the boxes we look for."
Palmer came through the ranks at the Pirelli Stadium, making 158 appearances in all competitions and helping them win promotion to the Championship. He netted gainst Rotherham last season.
Palmer had a loan spell at Oldham in 2016 where he made 14 appearances.
He will be available for selection in the Millers' next match at home to AFC Wimbledon a week on Saturday.