In Voices In My Head, players step into the courtroom and into the mind of a man on trial for robbing a bank. One player takes on the role of the prosecutor who is trying to convict the defendant, Guy, and send him to prison; everyone else takes on aspects of Guy's personality, such as Honesty or Selfishness, and attempts to influence the trial. To win the game, each player must achieve their hidden goal.

Each round, the prosecutor plays a trial card to present evidence, call witnesses, or grill Guy on the stand. Players then try to control Guy's actions by deploying control markers to a three-dimensional game board representing his brain. These actions will sway the jury in different ways and ultimately determine whether Guy goes free or is sent to prison.