For Young, it is a significant moment as he becomes the first player in Barclays Premier League history to win the award three times in a calendar year.
Manager O'Neill, a recipient of the monthly award for the sixth time, guided Villa to an unbeaten December which saw his side win four out of five games, including three away wins at Everton, West Ham United and Hull City.
Villa also impressively saw off the challenge of an in-form Bolton Wanderers side at Villa Park before a late Zat Knight strike held Arsenal to a 2-2 draw.
Young's emergence as one the most exciting players in the Barclays Premier League continued at pace throughout the month, scoring three goals and contributing two assists to end 2008 in style.
Two goals from the 23-year-old in a man-of-the-match display at Goodison Park, including a scintillating injury-time strike, saw off the challenge of Everton, while another goal from the England international capped a fine team display as the claret and blue troops defeated the Trotters.
A crucial assist, meanwhile, in the dying minutes of his side's game at Hull City's KC Stadium resulted in an own-goal which claimed maximum points.
The decision was made by the Barclays Awards Panel, which includes representatives from football's governing bodies, the media and fans.