Yumiko Kobayashi is a Japanese voice actress born on June 18, 1979, in Chiba Prefecture. She is a graduate of Wayo Women's University. Her career began in 1998 while she was still a college student, with her debut role as Mita in the drama CD Kirara. She gained early experience with supporting roles before landing her first lead role as Kento Yuki in the 2001 series Dennō Bōkenki Webdiver. Throughout her career, she has been affiliated with the agencies Murasu and Arts Vision, and has worked as a freelance voice actress since September 2007.

Kobayashi is widely recognized for her energetic portrayals of young male characters. A significant milestone in her career came in July 2018, when she succeeded Akiko Yajima as the voice of Shinnosuke Nohara, the titular protagonist of the long-running series Crayon Shin-chan. This role marked her as the second voice actress to take on the iconic character since the show began airing in 1992, and she has continued to voice Shinnosuke in subsequent television episodes and theatrical films.

Her extensive filmography includes a wide range of notable roles. She has had a long association with the Duel Masters franchise, voicing multiple characters including Shobu Kirifuda, Katta Kirifuda, and Joe Kirifuda across various series. In the Digimon franchise, she voiced Koushiro Izumi in Digimon Adventure: and Espimon in Digimon Ghost Game. Her other prominent television anime roles include Black Star in Soul Eater, Kazuma Azuma in Yakitate!! Japan, Gavroche in Les Misérables: Shōjo Cosette, Matake Ogata in the Shakugan no Shana series, Hachi in Mysterious Joker, Shiro in Hozuki's Coolheadedness, and Basil in A Little Snow Fairy Sugar. She has also appeared as Van in Ninjala, Ukitsu in Shin Ikki Tousen, and Taishi Koiwai in Drifting Home.

Beyond television, Kobayashi has voiced characters in numerous original video animations, such as Poemi Watanabe in Puni Puni Poemy and Souta Hori in Hori-san to Miyamura-kun. Her work in theatrical films includes roles in The Orbital Children as Hiroshi Tanegashima, as well as continuing her role as Shinnosuke Nohara in several Crayon Shin-chan films. In the field of dubbing foreign works, she provides the Japanese voice for characters such as Darwin Watterson in The Amazing World of Gumball.

Kobayashi was a member of the voice acting unit Prits, formed with Natsuko Kuwatani, Hisayo Mochizuki, and Nana Mizuki, all of whom voiced characters in the Sister Princess series. She has maintained close friendships with these fellow voice actresses since their time working together. She announced her marriage in April 2006 and has two children.