As a student of Southland Boys High School he was in the 1st XV for three years from 2004 to 2006 earning New Zealand Secondary Schools selection in his final year. The following year he was a member of the New Zealand Under 19 team which won the 2007 IRB World Championships in Ireland.
He made his Southland debut in 2007 against Otago, and emerged as a full-time starter during the 2009 Air New Zealand Cup, appearing in every match and scoring 3 tries. He continued to be a key member of the squad as the Stags defended the Ranfurly Shield for the greater part of the 2010 ITM Cup season. Another outstanding season with the Stags in 2011, in which they regained the Ranfurly Shield from Canterbury, saw him named Stags player of the year and also Southland Supporters Club player of the year for the second year.
Based on his strong performance in the 2009 Air New Zealand Cup, Hardie was included in the Highlanders squad for the 2010 Super 14 season. Serving mainly as backup to starting flankers Adam Thomson and Alando Soakai, he made 11 appearances over the course of the 13 game season, including three starts.
Hardie was named 2011 Stags player of the year.
In 2012, with the departure of Soakai to Japan, Hardie emerged as the starting openside flanker, but was sidelined with a serious toe injury.
While the Highlanders have had a poor 2013 season so far, Hardie has been one of teams outstanding performers, starting in all games this season, leading the team in tackles completed, pilfers and runs made.