Objective: To evaluate the safety, diagnostic yield, and ablation efficacy of a single-session workflow combining stereotactic percutaneous core-needle biopsy (CNB) immediately followed by microwave ablation (MWA) for liver tumors. Methods: We retrospectively reviewed consecutive patients (December 2021–May 2025) who underwent stereotactic CNB followed by MWA in the same procedure. Primary endpoints were primary technique efficacy (PTE) and complications. Secondary endpoints were 6-month local tumor progression (LTP) and diagnostic yield. Six-month LTP was summarized using a Kaplan–Meier (KM) point estimate with Greenwood 95% CIs. Results: Thirty-three patients underwent single-session biopsy and ablation (33 biopsied; 41 lesions ablated). PTE was 95.1% (39/41); two residual tumors were successfully re-ablated. Six-month LTP was 3.6% (patient level; KM 95% CI 0.0–10.5%) and 2.8% (lesion level; KM 95% CI 0.0–8.2%). There was one major complication (3%, post-ablation abscess) and no minor complications. Adequate tissue was obtained in all biopsies; a definitive diagnosis was established in 88% (29/33): malignancy in 73% (24/33) and benignity in 15% (5/33); 12% (4/33) were nondiagnostic. In the hepatocellular carcinoma (HCC)-suspected subgroup (LI-RADS LR-3 to LR-5; n = 24), all LR-5 lesions were HCC (11/11). Among LR-4 lesions (n = 7), histology showed HCC in 1/7 (14%) and cholangiocarcinoma in 2/7 (29%); 4/7 (57%) were benign or nondiagnostic. Among LR-3 lesions (n = 6), 2/6 (33%) were HCC and 4/6 (67%) were benign or nondiagnostic. In the metastasis-suspected subgroup (n = 9), malignancy was confirmed in 8/9 (89%); 1/9 (11%) was nondiagnostic. Conclusions: Single-session stereotactic CNB followed by MWA is feasible and safe, yields diagnostically useful tissue, and achieves high ablation efficacy.