Hagihara Hiroshi was born on June 27, 1926 in Kanazawa City, Ishikawa Prefecture. He graduated from the Department of Electrical Engineering, Faculty of Engineering, Kyoto University in 1950. After graduating, he joined NHK (Japan Broadcasting Corporation) Science & Technical Research Laboratories, and engaged in research related to electronic circuits, information theory, and communication systems. In 1957, he returned to the Faculty of Engineering, Kyoto University and started researching and developing computer systems.

In 1958, he became a project member for designing and developing the Kyoto University Digital Computer KDC-1. To achieve the goal of stable and robust operation of circuit elements, he worked on improving transistor circuits, increasing the reliability of hardware systems, and developing basic software systems. Upon project completion, he continued to work on improving the performance of computer systems, and started working on the microprogrammable asynchronous computer KT Pilot in 1961. This was the first Japanese computer to fully adopt the concept of microprogramming. KT Pilot can change its machine instruction set by using writable control storage based on magnetic thin-film memory; it achieved high-speed computation through the introduction of asynchronous operations. Based on KT Pilot, Toshiba developed the commercial computer TOSBAC-3400. Various language processors including assembler, FORTRAN and ALGOL60 compilers have been actually developed on this machine.

Looking for further performance improvements, he studied parallel processing, and in 1974, he developed QA-1, a computer with low-level register-ALU level parallelism, where one microinstruction controls quadruple ALUs simultaneously. He then turned to a large-scale successor called QA-2. Because of the salient feature of dynamic microprogramming, microprograms could be rewritten to flexibly adapt QA-1 and QA-2 to various research purposes including computer graphics, signal processing, and language processing.
In 1990, after his retirement from Kyoto University, he became a professor in the Faculty of Science and Technology, Ryukoku University. He is currently a president and a professor of the Kyoto College of Graduate Studies for Informatics. He was a director, a vice president and a president of Information Processing Society of Japan. From July 1994 to July 1997, he was a member of the Science Council of Japan and chaired the section for information science. He has published 22 books and book chapters, and 75 papers in academic societies.

He died on January 8, 2014.