Purpose: Patients with oligometastatic breast cancer (OMBC) may experience benefit from metastasis-directed therapy (MDT). Stereotactic body radiotherapy (SBRT) is highly ablative MDT that can be delivered with minimal toxicity. A multi-centre prospective pilot study was conducted to characterize SBRT in addition to systemic therapy in patients with both synchronous and metachronous OMBC. Materials and Methods: Included patients had newly diagnosed OMBC within 12 months of registration, with total metastatic disease burden limited to 5 extra-cranial sites or fewer, and received or initiated a standard systemic therapy, including chemotherapy, hormonal therapy, or targeted therapy at metastatic diagnosis. Diagnosis could be synchronous (de novo with primary disease in-situ) or metachronous (>12 months after previous diagnosis of Stage I-III breast cancer). Patients required controlled or radically treated primary disease. The primary outcome was successful accrual, planning and delivery of SBRT to all oligometastatic lesions. Patients were followed for 1 year post SBRT. Secondary outcomes including local recurrence, distant progression-free survival (DPFS) and quality of life (QoL) using European Organization for Research and Treatment of Cancer Core 30 Questionnaire were evaluated. An expected 90% (confidence interval 75-97%) successful treatment rate was required, resulting in a sample size of 30 patients. Results: Twenty-nine patients with 47 OMBC lesions were accrued from 2018-2022 which was delayed during the COVID epidemic. Median age was 52 (range 32-78). A majority of patients had estrogen (n=25, 86.2%) and progesterone receptor positive (n=19,65.5%), and Her2 Neu negative (n=24, 82.7%) breast cancers. Most patients had received chemotherapy either neoadjuvantly or adjuvantly (n=21,72.4%) and 55.7% (n=16) received hormonal therapy. The mean number of oligometastatic sites was 2 (range 1-5). Six patients had synchronous and 23 patients had metachronous OMBC. Twenty eight of 29 patients successfully completed planning and delivery, or 96.6%, meeting the primary endpoint. Twenty-four lesions received 5-fractions with median dose 30 Gy (IQR 30-35 Gy), while 23 lesions received two fractions with median dose 24 Gy (IQR 24-28 Gy). There were 26 spine metastasis, 12 non-spine bone metastasis, 4 liver metastasis, 4 nodal lesions, and one lung metastasis. There were 3 local recurrences (6.4% of lesions), at a median 352 days (range 149-390). There were 12 (41.3%) patients with a distant recurrence, including 2 with synchronous disease. Median DPFS was 388 days, (95% CI 335–NR). At study end, 3 (10.3%) patients had died of disease. No patients developed a Grade 3 or higher toxicity. Median QOL scores were 5.22 (4.73–5.72 95% CI) at baseline, which decreased to 4.8 (4.09-5.51 95% CI) on-treatment, and then increased to 5.3 (4.71-5.89 95% CI) at 3 months, and 5.33 (4.72-5.94 95% CI) at 6 months. Conclusions: SBRT is feasible to deliver in both synchronous and metachronous OMBC and appears to provide excellent local control with minimal toxicity and improvements in QOL. Further randomized studies are required to better characterize the role of SBRT in this population, particularly those with synchronous disease.