Jason Gillespie is a descendant on his father's side of the Kamilaroi people of Indigenous Australians, and is the first acknowledged Aboriginal person to become a Test cricketer. His mother has Greek heritage and Jason is the eldest of the five children. He attended Cabra Dominican College in Adelaide, South Australia. Gillespie married Anna (née McEvoy) in 2003. The couple have four children: Jackson (born February 2006), Brandon (born October 2007), Kingston (birthdate unknown) and daughter Delaney, born November 2012 in Yorkshire. Gillespie also has another daughter, Sapphire (born March 1995) from a previous relationship.

Gillespie is a vegan, and has criticized dairy farming and the use of leather balls. While coaching Yorkshire, Gillespie said of the club being sponsored by a dairy: "Yes, they are a sponsor but it doesn't mean I agree with what they do. It's out of my control, just like the fact that cricket balls are made of leather".

Gillespie made his first Australian domestic century in a Pura Cup match in the 2007/08 season against Tasmania. He put on a 250-run partnership with the South Australian wicketkeeper Graham Manou, who made 190. Gillespie remained 118 not out when the innings came to a close.

Gillespie made his first domestic first-class century exactly a year later on his 32nd birthday in a County Championship match versus Surrey at The Oval whilst playing for Yorkshire. He hit an unbeaten 123 and in doing so, alongside Tim Bresnan, set a record ninth-wicket partnership for Yorkshire. The pair put on 246 before Bresnan was stumped off the bowling of Nayan Doshi. Gillespie's 123 not out was also the highest score for Yorkshire by a number 10 batsman.

Bowling

Gillespie took 259 wickets in 71 Tests (at an average of 26.13) making him Australia's sixth-highest wicket-taker and giving him the 14th best bowling average for Australian bowlers who have taken more than a hundred wickets.

In terms of pace, he usually bowled at 140–150 km/h (87-93 mph) mark in his early career up to about 2001. When he made his comeback in the 2001/02 season, he bowled more consistently, but at a speed of about 135–145 km/h (84-90 mph). Consistent injuries forced Gillespie to operate from a shorter run-up and therefore reduce his pace.

Gillespie seldom dominated a Test series (the most wickets he took in a series is 20), but he was a reliable support bowler over