YUI began writing songs in ninth grade. At the age of sixteen on the recommendation of a friend she began studying songwriting and guitar at a private music school in her hometown of Fukuoka. Aspiring to become a professional, she carried her guitar around and sang at local places such as the seashore of Shingu and in the middle of rice fields at Kaminofu. Even though she was shy she still enjoyed doing street performances in the Tenjin district of Fukuoka.

Her professional career began in March 2004 when she sang three songs at an audition hosted by Sony Music Japan. Despite the audition rule that a participant could only sing two songs, all of the judges gave her the highest score possible which caused a fierce scramble among record labels to sign her. She first sang "Why Me" (a song later included in her major label debut single), followed by "It's Happy Line" and "I Know". "It's Happy Line" was her debut indie single with "I Know" as the b-side.

Upon leaving her hometown in Fukuoka for Tokyo, YUI wrote the song "Feel My Soul". She was planning its release on an indie label as a tribute to her hometown, when the song caught the ears of Fuji TV producer Mr. Yamaguchi, who just happened to see the demo video clip. He claimed that Yui's voice haunted him so much that he went out of his way to visit the recording studio all by himself. He even made his channel's prime time drama Fukigen na Gene use YUI's debut track.

On February 23, YUI released her first major debut single, "Feel My Soul" The music in Fukigen na Gene was mainly based on her songs such as 'Feel My Soul' and 'It's Happy Line'. With the drama tie-in "Feel My Soul" managed to sell over 100,000 copies. her next three singles, "Tomorrow's Way", "Life", and "Tokyo" did not chart as high as Feel My Soul did and were only moderately successful in comparison. After the release of four singles Yui released her debut album From Me to You, which is another moderate success with sales of more than 200,000 copies.


Midnight SunMany months later, YUI starred in a movie released on June 17, 2006, titled Taiyou No Uta-Midnight Sun, which was screened at the 2006 Cannes Film Festival. YUI's 5th single, "Good-bye Days", was written for this film and is by far her highest selling single at 200,000 copies sold. "I Remember You" her next single, did fairly well boosted by "Good-bye Days"' popularity. Soon after, YUI's 7th single "Rolling Star" was chosen by the anime series Bleach to be the 5th opening theme song; her third single, "Life", had previously been chosen as the 5th ending theme song. "Che.R.Ry", her 8th single, was used as a song for the KDDI au Listen Mobile Service CM. Her second album, Can't Buy My Love, fared well on the Oricon charts, staying for two weeks at #1 and shattering her entire previous album's record sales in one week. So far, Can't Buy My Love has managed to sell over 500,000 copies. Due to the success of Can't Buy My Love, Yui's previous album charted once again to add another 9k or so to the Oricon counting.

She released her 9th single, "My Generation / Understand", on 13 June 2007. This was the very first time that Yui released a double A-side single. My Generation is the theme song for the drama "Seito Shokun!", and Understand is the theme song for the movie "Sidecar ni Inu."

Her 10th single, "Love & Truth", released on September 26, is the theme song to Erika Sawajiri's film, Closed Note. Erika Sawajiri played Yui's role of Amane Kaoru in the TV series adaptation of Taiyou no Uta.

Her first Live DVD "Thank you My teens DVD" was released on November 14, 2007, which is a Live show video of Yui's 2nd Live show trip around Japan during the Spring of 2007.

On November 19, 2007, YUI opened her first Live show at Nippon Budokan. The tickets for the concert were sold out.

Her first single in 2008, Namidairo (English: Color of Tears), is set to be released for sale on February 27, 2008.

An as-yet unnamed album will be released in April.