The 19-year-old has taken over the mantle from Japan great Kohei Uchimura, Olympic all-around champion in 2012 and 2016, who chose not to defend his titles in Tokyo.
China’s Xiao Ruoteng was first heading into the last rotation.
But Hashimoto won gold with his high bar performance, finishing on 88.465.
Xiao finished with 88.065 to claim Silver and the Bronze Medal went to the Russian Olympic Committee’s Nikita Nagornyy, who posted a total of 88.031.
The two British athletes in the competition, James Hall and Joe Fraser finished eighth and ninth. Hall scored 84.598 and Fraser 84.499.
Fraser began the competition with high hopes of squeezing into the top three after qualifying in fifth place but an early fall on the pommel effectively put paid to his chances.
The 22-year-old, who is set to contest the individual parallel bars final next week, also stepped out on landing his vault.