1933年兵庫県芦屋市生まれ。戦後日本の前衛美術を牽引した吉原治良の息子であり、具体美術協会（具体）の創設メンバーとして活動した。1954年の第1回展から解散まで参加し、コールタールに砂や小石を散らした作品など、日常素材を用いた実験的表現で注目を集めた。さらに電球や蛍光灯、紙テープなど多様な素材を駆使し、表現の可能性を拡張し、その後もストライプなどを使った未来的な絵画表現を実現した。

Born in Ashiya, Hyogo Prefecture in 1933, Yoshihara was the son of Jiro Yoshihara, a leading figure in postwar Japanese avant-garde art, and a founding member of the Gutai Art Association (Gutai). He participated in the group from its first exhibition in 1954 until its dissolution, and attracted attention for his experimental use of everyday materials, such as works in which sand and pebbles were scattered over coal tar. He further expanded the possibilities of expression by making use of a variety of materials, including light bulbs, fluorescent lights, and paper tape, and later created futuristic paintings using stripes and other elements.