Background The 'Down to Test (DTT)' campaign is a sexually transmissible infection (STI) social marketing intervention delivered through outdoor music festival activations and supported by digital media communications in New South Wales, Australia. This paper investigates whether and how the tailored messages reached the intended audience. Methods Data was collected through three annual rounds of online surveys post campaign exposure, targeting young people (aged 15-29years) attending 14 music festivals in NSW from October 2017 to March 2020. Descriptive statistics, principal component analysis and multivariable logic regression were applied to identify the key client segment and factors associated with a strong intention for future STI screening. Results Of the 10044 participants with a valid urine specimen submitted, 261 (2.8%) tested positive for chlamydia. Altogether, 1776 participants (median age=22) self-completed the evaluation surveys online with more being female (73.4%) than male (26.2%). Participants were mostly Australian-born (89.5%), heterosexual (82.6%) and the majority being sexually active (96.7%). Rates of self-reported lifetime STI testing (70.4%) and intention for future STI screening ('definitely yes' in the next 12months, 39.0%) were also high. The most significant factor associated with future intention for STI testing is the Sexual Experience and Perception Factor (adjusted odds ratio [AOR]=2.02; 95%CI 1.76-2.32; P<0.001), followed by the Sexual Beliefs and Attitudes Factor (AOR=1.14; 95% CI 1.01-1.30; P<0.05). Conclusions The NSW state-wide DTT campaign has largely reached sexually active youth who are attentive to sexual health promotion messages and contributed to enhanced STI screening in a fun and peer-supportive environment.