Milner has been nominated for the gong, for players aged 23 and under at the start of the season, following his superb midfield displays for Villa this season.
Goalkeeper Hart has spent the campaign on loan at Birmingham from Manchester City and has been excellent between the sticks for Blues.
Manchester United striker Wayne Rooney and Arsenal midfielder Cesc Fabregas are the other players in contention.
Either could both join a very select band to lift the PFA player-of-the-year award and its young player prize in the same season.
Only Andy Gray (1977) and Cristiano Ronaldo (2007) have managed it before, with Rooney in line to become the first player to win the award three times, having already done so in 2005 and 2006.
PFA chief executive Gordon Taylor discussed the merits of Hart and Milner when announcing the nominees.
On Hart, Taylor said: "He has shown the benefits of the loan system. It is much better for him to be playing first-team football. I am really pleased he has been given that opportunity. He has not let Alex McLeish down and has the world in front of him."
As for Milner, Taylor continued: "I feel really proud of James. His parents came to us for help and advice from a very early age. He was determined to make it to the top. People have said he is a water-carrier. He is a lot more than that."