Simple Summary: Intracellular Ca2+ signaling is a critical factor in breast cancer metastasis. In the proliferation stage, increases in intracellular Ca2+ concentration through voltage-dependent Ca2+ channels, P2Y2 channels, transient receptor potential (TRP) channels, store-operated Ca2+ channels (SOCCs), and IP3 receptors and a decrease in intracellular Ca2+ concentration through plasma membrane Ca2+ ATPases and secretory pathway Ca2+ ATPases (SPCA) activate breast cancer cell proliferation. TRPM7, SOCC, inositol trisphosphate receptor (IP3R), ryanodine receptor (RyR), and sarco-/endo-plasmic reticulum Ca2+-ATPase (SERCA) increase the expression of epithelial-to-mesenchymal transition (EMT)-related proteins; meanwhile, SPCA and the Na+/Ca2+ exchanger (NCX) control the activation of EMT-related proteins. Increased Ca2+ through TRPC1, TRPM7/8, P2X7, and SOCC enhances breast cancer cell migration. The stromal interaction molecule (STIM)-Orai complex, P2X7, and Ca2+ sensing receptors are involved in invadopodia. Various pharmacological agents for Ca2+ channels have been proposed against breast cancer and have provided potential strategies for treating metastatic processes. Metastatic features of breast cancer in the brain are considered a common pathology in female patients with late-stage breast cancer. Ca2+ signaling and the overexpression pattern of Ca2+ channels have been regarded as oncogenic markers of breast cancer. In other words, breast tumor development can be mediated by inhibiting Ca2+ channels. Although the therapeutic potential of inhibiting Ca2+ channels against breast cancer has been demonstrated, the relationship between breast cancer metastasis and Ca2+ channels is not yet understood. Thus, we focused on the metastatic features of breast cancer and summarized the basic mechanisms of Ca2+-related proteins and channels during the stages of metastatic breast cancer by evaluating Ca2+ signaling. In particular, we highlighted the metastasis of breast tumors to the brain. Thus, modulating Ca2+ channels with Ca2+ channel inhibitors and combined applications will advance treatment strategies for breast cancer metastasis to the brain. [ABSTRACT FROM AUTHOR]