Tirabrutinib (Velexbru®) is an orally administered, small molecule, Bruton's tyrosine kinase (BTK) inhibitor being developed by Ono Pharmaceutical and its licensee Gilead Sciences for the treatment of autoimmune disorders and haematological malignancies. Tirabrutinib irreversibly and covalently binds to BTK in B cells and inhibits aberrant B cell receptor signalling in B cell-related cancers and autoimmune diseases. In March 2020, oral tirabrutinib was approved in Japan for the treatment of recurrent or refractory primary central nervous system lymphoma. Tirabrutinib is also under regulatory review in Japan for the treatment of Waldenström's macroglobulinemia and lymphoplasmacytic lymphoma. Clinical development is underway in the USA, Europe and Japan for autoimmune disorders, chronic lymphocytic leukaemia, B cell lymphoma, Sjogren's syndrome, pemphigus and rheumatoid arthritis. This article summarizes the milestones in the development of tirabrutinib leading to the first approval of tirabrutinib for the treatment of recurrent or refractory primary central nervous system lymphoma in Japan.