Introduction: Mind-body intervention (MBI) serves as a supportive aid in oncology. We hypothesized that MBI could impact the progression of chronic lymphocytic leukemia (CLL) in the “watch and wait” (w&w) phase. Methods: We conducted a non-randomized, prospective controlled study between the years 2020 and 2022 on 76 treatment-naïve CLL patients in the w&w phase. Thirty-seven patients were included in the intervention arm and received MBI, while 39 patients were included in the control group. The primary and secondary endpoints were prolongation of lymphocyte doubling time (LDT) and treatment-free survival (TFS). LDT was compared at 0, 180, 360, and 540 days using paired t tests. TFS was compared between the intervention and control groups using the log-rank test. Cox proportional hazards models were used to calculate the hazard ratio (HR) and 95% confidence interval (CI) for TFS in the intervention group compared to the control, stratified by the study covariates. Results: MBI prolonged LDT at all time points, including at day 360 (median of 2.47 years; CI 1.05–3.9; p = 0.001). TFS at 18 months was longer in the intervention group compared to the control group (HR 0.23; CI 0.06–0.79, p = 0.01). Conclusions: MBI was associated with prolonged LDT and TFS in patients with CLL in the w&w phase. These results provide a basis for a larger randomized controlled trial.