Fruit and vegetable (F&V) consumption is associated with a reduced risk of developing obesity and chronic diseases: however, only one in twenty Australian adults consume F&Vs at the recommended two servings of fruit and five servings of vegetables per day. What and how much people eat is influenced by their social and physical environments. Supermarkets are a key setting influencing food purchases, and as such, they can shape consumption patterns of F&Vs. Implementing effective strategies to increase F&V intake is crucial. The objective of this research was to test if shopper purchasing behaviour can be modified to purchase more F&Vs using social norm nudge messages (prompts) placed in shopping trolleys. Placards giving the message that the majority of shoppers purchased F&Vs at each shop were placed in shopping trolleys. Applying an intervention research design, 30 out of ~100 trolleys were fitted with the placards and shopper purchases were measured by collecting receipts to measure the quantity (kg), total and F&V spending (Australian dollars) for intervention versus control trolleys. We also conducted a short intercept survey that was administered independently from the research study day. Shoppers who selected trolleys with the social norm nudge placards (n = 109) purchased 1.25 kg more F&Vs (Intervention: mean = 5.45 kg, SD = 4.23 kg, 95% CI 4.65 kg, 6.26 kg vs. Control: mean 4.19 kg, SD = 3.75 kg, 95% CI 3.48 kg, 4.90 kg, p = 0.020, Cohen's d = 0.32) and spent an extra $9.10 more on F&Vs compared to shoppers in the control group (n = 109; Intervention: mean = $36.20, SD = $26.30, 95% CI = $31.24, $41.26 vs. Control: mean $27.10, SD = $24.00, 95% CI = $22.50, $31.67, p = 0.008, Cohen's d = 0.36). The social norm nudge placard shows promise in modifying shoppers' purchases to buy more F&Vs. Larger studies are required to elucidate and confirm these findings over the longer term.