Unlike most players in the AFL, Barlow did not play in the TAC Cup as a junior, but instead played for Shepparton United in the Goulburn Valley Football League, where he represented Victoria Country in 2007 as a 19-year-old. Barlow also won Shepparton United's best and fairest at age 19 before moving to the Victorian Football League (VFL) at the end of the 2007 season. He moved to play for the Werribee Football Club in the VFL in 2008. He had a very successful season in 2009, having moved from the forward line into the midfield, winning Werribee's best player award, the Fothergill–Round Medal as the league's best young player, came second in the 2009 J. J. Liston Trophy for the league's best and fairest player, and was named in the VFL's Team of the Year in both 2008 and 2009.
After training with St Kilda during the 2009 pre-season and with Essendon after the 2009 season, Barlow was drafted to Fremantle Football Club with their first selection in the 2010 Rookie Draft—the eighth overall. He was one of eight players from the VFL selected in the rookie draft. Alex Silvagni was also drafted to Fremantle from the Casey Scorpions. He also continued the trend of Fothergill–Round medallists being rookie listed, with all bar one of the previous seven winners being selected in the rookie draft: Michael Firrito (2002), Aaron Davey (2003), Adam Fisher (won the medal in 2004, rookie listed in 2003), Jason Davenport (2006), Shane Valenti (2007) and Robin Nahas (2008).
He made a successful debut for Fremantle in the opening round of the 2010 AFL season, gaining 33 possessions and kicking two goals, and was named as one of the best players on the ground. It was the most possessions gained by a player on debut since the AFL's official data partner, Champion Data, began collecting statistics in 1992, beating Bradd Dalziell's 32 possessions in 2008. In his first Derby (R6 2010), Barlow was awarded the Ross Glendinning Medal for being the best player on the ground. His game consisted of 10 kicks, 15 handballs, 4 marks, 8 tackles and a goal.
A broken leg ended Barlow's season in Round 14 against Port Adelaide: late in the final quarter of the game, an awkward collision with teammate Rhys Palmer saw Barlow cleanly break both the tibia and fibula in his left leg, a few inches below the knee.