Reid was taken with Collingwood's first pick in the 2006 AFL Draft, pick number eight, and was handed the number 20 guernsey which was vacated by Chris Tarrant, after he was traded to the Fremantle Dockers. Reid made his Collingwood debut in Round 13, 2007 against Hawthorn, aged 18 years and 2 months. He was the youngest player in the AFL at the time. Originally recruited as a forward, he is now recognised as one of the best key defenders in the game. He previously played for the Murray Bushrangers, Wangaratta Rovers and Bright Junior Football Club.
Prior to 2010 Reid had only played a cumulated total of 8 games from 2007 to 2009. 2010 would become his breakout year when he went on to play 21 games out of a possible 26. In round 12 he was nominated for the AFL Rising Star award, and went on to finish 10th overall. Reid played in both Grand Finals opposite St Kilda'sJustin Koschitzke. In the Grand Final replay Reid suffered a leg injury, but wanted to play on and finish the game. It was later discovered that he had continued to play with a fractured fibula.