Yui Watanabe is a Japanese voice actress and singer born on December 4, 1988, in Minoh, Osaka Prefecture. Her path to a voice acting career began during high school when she won the JTB Award at a Voice Newtype magazine audition, which provided a pathway into the industry despite initial family concerns. To fund her move to Tokyo and pursue her dream, she worked multiple part-time jobs. She entered the JTB Entertainment Academy in 2008 and, in August 2009, joined the female idol unit Hoshi no Otome Kagekidan. After graduating from the training school, she affiliated with a talent agency and made her professional debut in October 2010 as the voice of Sorakara-chan, the official character for the Tokyo Skytree. She also became a regular on the television program Hougen Kanojo around this time.

Watanabe's career encompasses a wide range of anime television series and films. She is known for her role as Yuri Oshimoto in the long-running comedy series Teekyū and its various spin-offs, including Takamiya Nasuno Desu! and Usakame. She provided the voice for Mikan Shiratama across the PriPara multimedia franchise, appearing in the main television series, multiple films such as Gekijō-ban PriPara Mi~nna Atsumare! Prism Tours and Tobidasu PriPara ~Miina de Mezase! Idol Grand Prix, and the game Idol Land Pripara. She voices the character Winning Ticket in the Uma Musume Pretty Derby franchise, including the second season of the anime, the special BNW no Chikai, and related series like Umayuru and Umayon. Other notable anime roles include Akane Yonomori in Engaged to the Unidentified, the title character Akae in Chikasugi Idol Akae-chan, Rinko in Wasimo, Minako Nitta in Cinderella Nine, Nyurunyan in Nyuru Nyuru!! Kakusen-kun 2-ki, Macaron in 30-sai no Hoken Taiiku, and Laval in the Japanese dub of Lego Chima ~Animal Senshi-tachi no Densetsu~. In film, she voiced Nao Yokoyama in THE IDOLM@STER MOVIE: Kagayaki no Mukōgawa e!.

A significant and recurring role in her career is Nao Yokoyama in The iDOLM@STER franchise, beginning with the game The Idolmaster Million Live! and continuing in its anime adaptation and the game The Idolmaster Million Live! Theater Days. This role has been a central part of her work, involving live performances and recordings with other cast members. In video games, her roles include Rui Kamijo in Girlfriend (Kari) and voicing various characters in mobile and social games.

Alongside her voice acting, Watanabe has pursued a music career. She made her solo CD debut in February 2011 with the single Secret Melody. She sang her first anime theme song for Teekyū in 2012 and has since released several singles, including happysmileangel, Kizuna, and DREAM☆TRAVELER, and an album titled FUN FAN VOX, which has charted on the Oricon charts. Her musical contributions also extend to performing theme songs for series she appears in, such as Million Doll.

Throughout her career, Watanabe has been affiliated with different agencies, including JTB Entertainment and Dandelion, and as of 2024, she is affiliated with Kenyu Office. She maintains friendships with fellow voice actors, notably Rei Matsuzaki, with whom she shares a passion for baseball, and Aina Kusuda, with whom she has worked on various projects and radio programs. Her hometown of Minoh appointed her as a special voice actor ambassador in November 2016. A notable aspect of her personal background is her athletic history; she was an accomplished tennis player during her school years, winning several regional championships, and once considered becoming a physical education teacher.