Background/Objectives: Enhanced recovery after surgery (ERAS) protocols optimize perioperative care and improve recovery. This study evaluated the effectiveness of ERAS in one- or two-level posterior lumbar fusion surgeries, focusing on perioperative medication use, pain management, and functional outcomes. Methods: Eighty-eight patients undergoing lumbar fusion surgery between March 2021 and February 2022 were allocated into pre-ERAS (n = 41) and post-ERAS (n = 47) groups. Outcomes included opioid and antiemetic consumption, pain scores (numerical rating scale (NRS)), functional recovery (Oswestry Disability Index (ODI) and EuroQol 5 Dimension (EQ-5D)), and complication rates. Pain was assessed daily for the first four postoperative days and at 6 months. Linear Mixed Effects Model analysis evaluated pain trajectories. Results: The post-ERAS group showed significantly lower opioid (p = 0.005) and antiemetic (p < 0.001) use. No significant differences were observed in NRS pain scores in the first 4 postoperative days. At 6 months, the post-ERAS group reported significantly lower leg pain (p = 0.002). The time:group interaction was not significant for back (p = 0.848) or leg (p = 0.503) pain. Functional outcomes at 6 months, particularly ODI and EQ-5D scores, showed significant improvement in the post-ERAS group. Complication rates were lower in the post-ERAS group (4.3% vs. 19.5%, p = 0.024), while hospital stay and fusion rates remained similar. Conclusions: The ERAS protocol significantly reduced opioid and antiemetic use, improved long-term pain management and functional recovery, and lowered complication rates in lumbar fusion patients. These findings support the implementation of ERAS protocols in spinal surgery, emphasizing their role in enhancing postoperative care.