Tomohiro Yamaguchi is a Japanese voice actor born on December 26, 1987, in Tokyo. He is affiliated with the Tokyo Actor's Consumer's Cooperative Society, commonly known as Haikyō. Prior to joining Haikyō, he was associated with the agency B-Box until March 2023. He began his entertainment career not as a voice actor, but as a singer, making his debut in 2009 as a vocalist for voyager, a group known for performing theme songs for Ultraman series, while he was still a student at Chuo University.

Yamaguchi's early voice acting roles included minor parts in long-running series such as Bleach and Penguindrum. In 2014, he voiced the character M. Kirito Kiritani in the card game comedy anime Gigant Shooter Tsukasa. A significant early role was Marin Hollow, a mage from the Alvarez Empire, in the final season of the popular fantasy series Fairy Tail. This period also saw him take on his first name role change; he was credited as Tomohiro Yamaguchi (山口智大) until March 2017, when he changed the spelling of his stage name to its current form, 山口智広.

The late 2010s and early 2020s saw Yamaguchi in a wide variety of supporting roles across numerous anime series. He appeared in productions such as Your Name., Banana Fish, and Jujutsu Kaisen. He voiced the AI robot Puff Puff in Tomica Kizuna Gattai Earth Granner and took on the role of Sōsuke Sugaya in the Ansatsu Kyōshitsu franchise. In 2021, he voiced one of Odin's two raven companions, Muninn, in the Netflix series Record of Ragnarok. The following year, he began voicing the character Ururun in the children's anime series PuniRunes, a role he continued into the show's third season in 2025.

Yamaguchi has continued to build an extensive filmography with consistent work. His credits in the mid-2020s include roles in Oshi no Ko, Shangri-La Frontier, and as the voice of a miniature version of Piccolo in Dragon Ball Daima. He has frequently appeared in productions alongside fellow voice actors such as Handai Musou, Ayaka Asai, and Kentaro Ito, indicating recurring collaborations within the industry. His career demonstrates a steady progression from minor roles to recognizable characters in major franchises.