Holness has put pen to paper on a two-year deal following his release by Rochdale, where he played alongside new Albion team-mate Nathan Stanton when they won promotion from League Two in 2009/10.
"Marcus is very strong and he is hungry to get his career back on track," said Burton boss Gary Rowett. "He has shown a real desire to come to Burton and he has played 80 game in League One over the past two seasons.
"At 23 he is the right age as well to be adding to the squad."
Holness has been training with Albion and scored an own goal on Saturday as Aston Villa beat Rowett's side 2-1 at the Pirelli Stadium in a pre-season friendly.