Introduction and objectives In out-of-hospital cardiac arrest, early recognition, calling for emergency medical assistance, and early cardiopulmonary resuscitation are acknowledged to be the three most important components in the chain of survival. However, bystander basic life support (BLS) initiation rates remain low. The objective of the present study was to evaluate the association between bystander BLS and survival after an out-of-hospital cardiac arrest (OHCA). Methods We conducted a retrospective cohort study of all patients with OHCA with a medical etiology treated by a mobile intensive care unit (MICU) in France from July 2011 to September 2021, as recorded in the French National OHCA Registry (RéAC). Cases in which the bystander was an on-duty fire fighter, paramedic, or emergency physician were excluded. We assessed the characteristics of patients who received bystander BLS vs. those who did not. The two classes of patient were then matched 1:1, using a propensity score. Conditional logistic regression was then used to probe the putative association between bystander BLS and survival. Results During the study, 52,303 patients were included; BLS was provided by a bystander in 29,412 of these cases (56.2%). The 30-day survival rates were 7.6% in the BLS group and 2.5% in the no-BLS group (p < 0.001). After matching, bystander BLS was associated with a greater 30-day survival rate (odds ratio (OR) [95% confidence interval (CI)] = 1.77 [1.58–1.98]). Bystander BLS was also associated with greater short-term survival (alive on hospital admission; OR [95%CI] = 1.29 [1.23–1.36]). Conclusions The provision of bystander BLS was associated with a 77% greater likelihood of 30-day survival after OHCA. Given than only one in two OHCA bystanders provides BLS, a greater focus on life saving training for laypeople is essential.