Methods: WC recipients undergoing single-level MIS TLIF were identified. PROMs of Visual Analog Scale (VAS) for back and leg pain, Oswestry Disability Index (ODI), 12-item Short Form Physical and Mental Composite Scale (SF-12 PCS/MCS), and Patient-Reported Outcomes Measurement Information System Physical Function evaluated subjects preoperatively/postoperatively. Subjects were grouped according to preoperative SF-12 MCS: <41 vs. ≥41. Demographic/perioperative variables, PROMs, and MCID were compared using inferential statistics. Multiple regression was used to account for differences in spinal pathology. Results: The SF-12 MCS <41 and SF-12 MCS ≥41 groups included 48 and 45 patients, respectively. Significant differences in ΔPROMs were observed at SF-12 MCS at all timepoints, except at 6 months (p≤0.041, all). The SF-12 MCS <41 group had worse preoperative to 6-months SF-12 MCS, 12-weeks/6-months VAS back, 12-week VAS leg, and preoperative to 6-months ODI (p≤0.029, all). The SF-12 MCS <41 group had greater MCID achievement for overall ODI and 6-weeks/1-year/overall SF-12 MCS (p≤0.043, all); the SF-12 MCS ≥41 group had greater attainment for 6-month VAS back (p=0.004). Conclusions Poorer mental functioning adversely affected the baseline and intermediate postoperative quality-of-life outcomes pertaining to mental health, back pain, and disability among WC recipients undergoing lumbar fusion. However, outcomes did not differ 1–2 years after surgery. While MCID achievement for pain and physical function was largely unaffected by preoperative mental health score, WC recipients with poorer baseline mental health demonstrated higher rates of overall clinically meaningful improvements for disability and mental health