Kaulitz was born on 1 September 1989 in Leipzig, East Germany. He has an identical twin brother, Tom, who is older by ten minutes. His parents, Simone Kaulitz and Jörg W., separated when Kaulitz was seven years old. Simone married Gordon Trümper, the guitarist from German rock band Fatun on 1 August 2009, after dating for 12 years. Kaulitz showed an early interest in singing, as did Tom in playing guitar. Trümper noticed the twins' musical inclinations, and helped the twins to start their own band. According to Kaulitz in several interviews, he and Tom started writing music at the age of seven years.

At the age of 10, the twins began playing live in Magdeburg , with a name for their duet called "Black Question Mark" near their hometown of Loitsche , doing small venue shows and were largely unknown. The band lacked a drummer and bass player and the twins relied on a keyboard to fill in other instrumental sounds.

The year the brothers turned 12, they met Georg Listing (then 14) and Gustav Schäfer (then 13) in the audience of one of their shows. Listing and Schäfer were friends and, after the show, having liked what they heard and saw, made an offer to join. The band was promptly renamed "Devilish" due to an article published at the time that referred to their "devilishly great"sound. So Devilish was born as a band. Initially, Devilish was going nowhere, until Bill Kaulitz appeared on the German version of the reality talent show Star Search, thanks to a bet he lost against his brother. The group, founded in 2001, changed its name to Tokio Hotel after signing with Sony in 2003.

n 2005, David Jost arranged a meeting between the band and Universal Music Group and Interscope records and they signed. They began working immediately, releasing their debut LP Schrei later that year. Their first single from Schrei was Durch den Monsun , which peaked at #1 in Germany after a month of its release.

Tokio Hotel launched their debut tour in Germany, to support the release of Schrei and its singles. They toured Germany and also recorded a live DVD. In 2006, Bill Kaulitz voiced the role of Arthur in the first part of the German version of the film Arthur and the Invisibles.

Tokio Hotel were a household name in Germany at this point, and this compelled the band to return to the studio. After the success of Schrei, Tokio Hotel began working on their second album, Zimmer 483 (Room 483), released in February 2007. The album spawned three singles initially: "Übers Ende der Welt" ("Over the End of the World" – released as "Ready, Set, Go!"), "Spring nicht" ("Don't Jump"), and "An deiner Seite (Ich bin da)" ("By Your Side (I am there)" – released as "By Your Side"). A fourth single, "Heilig" ("Holy" – released as "Sacred"), was released in 2008.

To support the release of Zimmer 483, In 2008, Tokio Hotel came to the United States for 5 shows, starting in Canada and ending in New York . Tokio Hotel was the first German group since Nena to have international success and maintain their status. The US tour was a success, but disaster struck when they came to Europe for their 1000 Hotels Tour.

As Tokio Hotel's fanbase increased in the Western part of the world, Kaulitz and the band decided to re-record select songs from both Schrei and Zimmer 483 for a new English-language LP so that fans around the world could understand the band's songs. The result of these re-recorded songs was Tokio Hotel's debut English album, titled Scream. The album was released in Europe in mid-2007, however it did not reach release in the West until mid-2008.

Scream spawned four singles: Scream (cover of Schrei ), Monsoon (cover of Durch den Monsun ), Don't Jump (cover of Spring Nicht ) and Ready, Set, Go! (cover of Übers Ende der Welt ). Scream was a moderate success internationally, and to support the release, Tokio Hotel left Europe for the first time and flew to the United States.

In 2008, Tokio Hotel came to the United States for 5 shows, starting in Canada and ending in New York . Tokio Hotel was the first German group since Nena to have international success and maintain their status. The US tour was a success, but disaster struck when they came to Europe for their 1000 Hotels Tour.

The 1000 Hotels Tour began in Brussels, Belgium, on 3 March 2008, and was set to continue through the Netherlands, Luxembourg, France, Spain, Portugal, Italy, and Scandinavia, ending on 9 April. However eleven days after the start of the tour, on 14 March, Kaulitz began to experience voice problems in the middle of a show in Marseille, France. He let the audience sing more often and the band cut their set down from twenty-one to sixteen songs.

Two days after the incident in France, Tokio Hotel cancelled a show in Lisbon, Portugal moments before it was to commence. The band, with the exception of Kaulitz, came on the stage and apologized for the show being cancelled. They explained that Kaulitz was sick and was being flown back to Germany to see a specialist: he had played forty-three shows without a break and had developed an untreated throat infection. The infection caused a cyst to develop on the singer's vocal cords that had to be removed via larynx surgery on 30 March. Kaulitz was unable to speak for ten days afterwards and had to undergo speech therapy for one month. It was a tough time for the Tokio Hotel frontman, who doubted whether he would ever be able to sing like he used to again.

By May 2008, Kaulitz had sufficiently recovered and Tokio Hotel rescheduled the 1000 Hotels Tour dates, adding several open-air concerts. The tour concluded on 13 July 2008 in Werchter, Belgium, and, despite the surgery and time taken off, was deemed a success.

Over 2008 and 2009, Tokio Hotel returned to the recording studio to record their second English album and third German album. The result was Humanoid, which was a much more techno-oriented release and a new sound. Humanoid was released on 6 October 2009, and just short of a month later Tokio Hotel picked up the "Best Group" award at the EMAs in Berlin on 5 November. Humanoid has so far spawned two singles, "Automatic"/"Automatisch", released in September 2009, and "World Behind My Wall"/"Lass uns laufen" (meaning "Let Us Run"), to be released in January 2010.

On October 3, 2014, the band released the album that would break a 5-year silence. Kings of Suburbia was only released in English (not like their previous works, in English and German). The singles were, in order, Run, Run, Run , Girl Got a Gun , both promotional, and Love Who Loves You Back with Feel It All being the official singles. The album reached number one in 30 countries and entered the top 5 in another 17 countries, being considered a success despite the time elapsed, in which the twins moved to Los Angeles to escape the German media scene.

On September 1, 2016, the band released a post on Instagram , where they would confirm a tour in early 2017 to promote their album Dream Machine. Which has songs like Something new , What if , both promotional, and Boy don't cry , the latter released on October 20, 2017. The songs from the album are all on their official YouTube account.

Tokio Hotel announced their new tour for Autumn 2021, Beyond the World, on 7 December 2020. This was later postponed until April 2022 due to the COVID-19 pandemic, and again until April 2023 due to the Russo-Ukrainian War.

Kaulitz announced on 11 January 2021 via Tokio Hotel's official Facebook and Instagram accounts their new single "White Lies", which will feature a guest appearance from German EDM duo VIZE. This was released on 15 January 2021. Other 2021 releases by Tokio Hotel include The Who cover "Behind Blue Eyes"; also with VIZE in May, "Sorry Not Sorry" with German rapper Badchieff in August, and "Here Comes the Night" in October.

Tokio Hotel announced their new single "Bad Love", which was originally to be released on 21 January 2022, but was postponed due to Bill and Tom Kaulitz being unable to arrive in Germany in time for the promotion. This was eventually released on 4 February 2022 with new singles "HIM", "When We Were Younger", "Fahr mit mir (4x4)" with Kraftklub and "Happy People" with Daði Freyr following on 8 April 2022, 27 May 2022, 8 July 2022 and 21 October 2022 respectively. Their seventh studio album, 2001, was released on 18 November 2022.