Active travel can have health and environmental benefits. This study evaluated the impact of a month-long (October 2015) campaign encouraging primary school children in Victoria, Australia to engage in active school travel. With support from local councils, schools participated in the campaign by monitoring active school travel and delivering promotional activities. A longitudinal study evaluated campaign impact. Carers (n = 715) of Victorian primary school children were recruited via social media and completed online surveys at baseline (T1; 0 wk) and during (T2; +2 wks) and after the campaign (T3; +6 wks). Carers reported their child's travel behaviour over the last five school days, and whether their child and/or their child's school participated in the campaign. Separate generalised linear models were used for T2 and T3 outcomes adjusting for T1 values and potential confounders. A greater proportion of children who participated in the campaign engaged in any active school travel at T2 (OR = 2.49, 95% CI = 1.63, 3.79) and T3 (1.62, 95% CI = 1.06, 2.46) compared with non-participating children. Similarly, these children had a higher frequency of active school travel at T2 (IRR = 1.60, 95% CI = 1.29, 1.97) and T3 (IRR = 1.45, 95% CI = 1.16, 1.80). Campaign participation resulted in small, short-term increases in active school travel.