Kengo Kawanishi is a Japanese voice actor born on February 18, 1985, in Osaka Prefecture. He graduated from the AMUSEMENT MEDIA General Academy's voice actor program in 2005 and made his professional debut in 2006. Initially affiliated with Office Kaoru, he became a member of Mausu Promotion on February 1, 2013, where he continues his career.

Kawanishi's career progressed through various supporting roles before he landed his first leading role in an anime series as Mikazuki Augus in Mobile Suit Gundam: Iron-Blooded Orphans in 2015. This performance is widely considered his breakout role. In 2016, he took on another significant leading role as Rei Kiriyama in March Comes in like a lion. Chika Umino, the original author of March Comes in like a lion, described his voice as "a shining dark voice," capturing the essence of his nuanced performance.

His filmography is extensive and includes a wide array of characters across many popular series. Some of his most notable roles include Gen Asagiri in the Dr. Stone franchise, a role he has played across multiple seasons including Stone Wars, Ryusui, and New World. He also voices Muichirō Tokitō in Demon Slayer: Kimetsu no Yaiba, appearing in the Swordsmith Village Arc and Hashira Training Arc. He has been a recurring presence in the Fruits Basket reboot, playing Ritsu Soma across multiple seasons.

Kawanishi has demonstrated his versatility by taking on roles in nearly every genre. He has played Eita Otoya in BLUELOCK, Nahoya Kawata in Tokyo Revengers, Sōshirō Hoshina in Kaiju No. 8, Junta Shiraishi in Kubo Won't Let Me Be Invisible, Lye Batenkaitos in Re:ZERO -Starting Life in Another World-, and Roshō Tsutsujimori in the Hypnosis Mic -Division Rap Battle- projects. His work also includes roles like Quaiesse Hazeia Quintia in Overlord IV, Sekt in Skeleton Knight in Another World, Shiden Ritter in Scarlet Nexus, Tell Kawai in Yu-Gi-Oh! Go Rush!!, and numerous others such as Gekkō Itabashi in Doreiku The Animation, Hiro Okamachi in The Gymnastics Samurai, Tomoya Chinami in The Girl in Twilight, Kōsuke Sakaki in Run with the Wind, Junichi Hagio in Mr. Tonegawa, Sora Hikurakawa in Jingai-san no Yome, Hu Li in Voice of Fox, Inyō in Ultramarine Magmell, Natsusa Yuzuki in number24, Honeyguide in Africa Salaryman, Tōru Kishiri in Fire Force, Narugami in Interspecies Reviewers, Almanfi in Mushoku Tensei: Jobless Reincarnation, Shôji Satô in Food Wars! Shokugeki no Soma: The Fourth Plate, Roland in The Case Study of Vanitas, Kaede Hatori in the film Blue Thermal, Nansen Ichimonji in Toku Touken Ranbu: Hanamaru ~Setsugetsuka~, Manfred in The Genius Prince's Guide to Raising a Nation Out of Debt, Haruka Hashida in Blue Period, Kō in Caressing the Nipples of My Hibernating Bear, Roi in KING’S RAID: Successors of the Will, Dai-kun in Zonmi-chi: Meat Pie of the Dead, Mash in Cautious Hero: The Hero Is Overpowered but Overly Cautious, Seijirō Kanmuri in AMAZING STRANGER, Gunha Sogiita in A Certain Scientific Railgun T, Izuru Nikki in Kiss Made, Ato 1-Byō., Ken Yamamura in The iDOLM@STER SideM: 315 Variety Pack! Made In Passion!, Fudōmyō Ō in Namu Amida Butsu! -Rendai Utena-, Shoji Sato in Food Wars! The Third Plate, Akira Kagetsuki in the Monster Strike the Animation projects, Gael in Heroes ~Legend of Battle Disks~, Red Robin in Batman Ninja, Shuto Kirishima in Oblivion Battery, Erland Martonen in Yakitori: Soldiers of Misfortune, Haru Welt in Zegapain STA, and the character Prince in Tower of God: Workshop Battle. He has often been noted for a vocal tone that some listeners find similar to that of fellow voice actor Akira Ishida, whom Kawanishi has cited as someone he looks up to.