Nigella sativa, commonly referred as black cumin, is a popular spice that has been used since the ancient Egyptians. It has traditionally been used for treatment of various human ailments ranging from fever to intestinal disturbances to cancer. This study investigated the apoptotic, antimetastatic, and anticancer activities of supercritical carbon dioxide (SC-$CO_2$) extracts of the seeds of N. sativa Linn. against estrogen-dependent human breast cancer cells (MCF-7). Twelve extracts were prepared from N. sativa seeds using the SC-$CO_2$ extraction method by varying pressure and temperature. Extracts were analyzed using FTIR and UV-Vis spectrometry. Cytotoxicity of the extracts was evaluated on various human cancer and normal cell lines. Of the 12 extracts, 1 extract (A3) that was prepared at $60^{circ}C$ and 2500 psi (~17.24 MPa) showed selective antiproliferative activity against MCF-7 cells with an $IC_{50}$ of 53.34-2.15 ${mu}g/mL$. Induction of apoptosis was confirmed by evaluating caspases activities and observing the cells under a scanning electron microscope. In vitro antimetastatic properties of A3 were investigated by colony formation, cell migration, and cell invasion assays. The elevated levels of caspases in A3 treated MCF-7 cells suggest that A3 is proapoptotic. Further nuclear condensation and fragmentation studies confirmed that A3 induces cytotoxicity through the apoptosis pathway. A3 also demonstrated remarkable inhibition in migration and invasion assays of MCF-7 cells at subcytotoxic concentrations. Thus, this study highlights the therapeutic potentials of SC-$CO_2$ extract of N. sativa in targeting breast cancer.