Background: Postoperative pain is a major challenge for patients undergoing breast reconstruction after surgical treatment of breast cancer, resulting in prolonged hospitalizations and additional resource utilization. Evidence on the efficacy of techniques to minimize postoperative pain in autologous breast reconstruction is lacking. We sought to determine whether preoperative paravertebral block (PVB), a regional anesthetic technique, affects postoperative pain control and hospital length of stay (LOS) in patients undergoing autologous breast reconstruction. Methods: Consecutive patients undergoing postmastectomy autologous breast reconstruction between 2012 and 2015 were identified from a prospectively collected database to compare those who received PVB to those who did not. Primary outcomes included self-reported pain score, time to oral-only narcotic usage (TTON), and LOS. Sample differences were compared using Wilcoxon rank-sum and Chi square tests for continuous and categorical variables. Kaplan–Meier analysis was used to evaluate TTON and LOS, with Mantel-Cox test used to compare groups. Results: Of 78 patients, 39 received PVB and 39 did not. Study groups did not differ regarding age, body mass index, American Society of Anesthesiologists class, mastectomy type, flap type, or cancer stage (p > 0.05). Patients in the PVB group reported significantly lower postoperative pain at 2 (p < 0.01) and 24 h (p < 0.01) and shorter median TTON (66 vs. 76 h, p < 0.01). Importantly, median LOS was reduced for patients receiving a PVB in both hours (95 vs. 116, p < 0.01) and hospital nights (4 vs. 5, p = 0.05). Conclusions: Preoperative PVB is associated with improved postoperative pain control and shorter hospitalizations for patients with breast cancer undergoing postmastectomy autologous reconstruction.