β-Tricalcium phosphate (β-TCP) has been extensively used in bone tissue engineering in the form of scaffolds, granules, or as reinforcing phase in organic matrices. Solid-state reaction route at high temperatures (>1000 °C) is the most widely used method for the preparation of β-TCP. The high-temperature synthesis, however, results in the formation of hard agglomerates and fused particles which necessitates postprocessing steps such as milling and sieving operations. This, inadvertently, could lead to introducing unwanted trace elements, promoting particle shape irregularity as well as compromising the biodegradability and bioactivity of β-TCP because of the solid microstructure of particles. In this study, we introduce a one-pot wet-chemical method at low temperatures (between 160 and 170 °C) to synthesize hollow β-TCP (hβ-TCP) submicron particles of an average size of 300 nm with a uniform rhombohedral shape. We assessed the cytocompatibility of the hβ-TCP using primary human osteoblasts (HOB), adipose-derived stem cells (ADSC), and antigen-presenting cells (APCs). We demonstrate the bioactivity of the hβ-TCP when cultured with HOB, ADSC, and APCs at a range of particle concentrations (up to 1000 μg/mL) for up to 7 days. hβ-TCP significantly enhances osteogenic differentiation of ADSC without the addition of osteogenic supplements. These findings offer a new type of β-TCP particles prepared at low temperatures, which present various opportunities for developing β-TCP based biomaterials.