The Sheffield Wednesday man joins ex-Leeds United star White at the New York Stadium.
Rotherham United have been busy this week, signing a completely different left-hand side in the past few days - both from Yorkshire rivals.
Earlier in the week they snapped up Aidy White from Leeds United. The Leeds veteran had struggled with injury throughout last season and when his contract expired this summer Rotherham took the opportunity to snap up the talented left-sided player.
One question that would need to be answered about his role at Rotherham was whether he would play at let-back or on the left-wing. Yesterday's new summer signing was Joe Mattock. The former West Brom defender arrived on a free transfer from Sheffield Wednesday, which would seem to hint that White will be operating a left-wing role.
Mattock, a former England under-21 international, will arrive for business on the same day as White, July 1st.
Rotherham United are hoping to push on next season after surviving the drop to League One last term.
The acquisition of two experienced Championship operators from Yorkshire rivals is a shrewd move from Millers boss Steve Evans and a left-hand side of Mattock and White should help them toward survival once again.