The Welsh Under 21 International left Ipswich last month and verbally agreed to join the Millers before his summer holidays, MillersMAD understands.
Despite no official announcement yet by the club, Brown is expected to link up with his new team mates at some point this week as the players and staff return for pre-season.
Meanwhile the departure of midfielder Nicky Law to Scottish outfit Motherwell is also set to be confirmed shortly.
Law turned down a new contract last month ending a two year stay at Don Valley after joining from neighbours Sheffield United. He will move north for a minor undisclosed fee as he is under 24.