Adopted at the age of 6 months, Gardiner was born in Melbourne and grew up in rural Victoria. He was bullied at school for being homosexual and suffered from anorexia for two years until he came to terms with his sexuality at the age of 16.
At 12, he wrote and submitted his first musical and was the youngest ever applicant to attend The Workshop in Sydney.
Gardiner has lived a varied and colourful life which has spanned theatre, film, TV and cabaret. Having started aged 16, he began his professional career in the original Australian cast of 42nd Street and then went on to perform in over 20 award winning musicals over the past 17 years in three continents.
Whilst Gardiner was performing in The Royal National Theatre's award-winning production of the Cole Porter hit Anything Goes in 2004, he was cast as the Culture Guru for the UK version of Queer Eye For the Straight Guy on LIVINGtv and Channel 4. He tried doing the two jobs simultaneously for 8 weeks and ended up in hospital due to fatigue and was forced to make a decision over which to keep; he chose to pursue a career in TV. Gardiner is currently a judge on ITV's Dancing on Ice in the UK having returned in 2013 after being dropped from the 2012 series after ITV received a large amount of complaints about his unnecessary cutting insults of numerous contestants. He is often at odds with the other judges (in particular the Ex-Professional Ice Skaters) because of his negative attitude towards the celebrity competitors. He also appears on Nine Network's Torvill and Dean's Dancing on Ice in Australia as a judge on the panel. Jason is currently the fashion expert for ITV's This Morning, and has also appeared on ITV's Loose Women @ 5.30! and on the panel of Born To Shine.