He grew up in Leipzig with his first-born, identical twin brother Tom. His parents, the painter Simone Charlotte Kaulitz and the truck driver Jörg W., separated when he was six years old. The mother then moved with her two sons to Loitsche near Magdeburg to live with her new partner, the musician Gordon Trümper. As children they were seen in the Radio Bremen production "Verkehrt nach dir". Both found their passion for music as children, which they worked on together from then on. Tom learned to play guitar at the age of ten, while Bill Kaulitz concentrated on singing. They were supported musically by their stepfather, who was himself an active musician in Magdeburg. While performing at a club in Magdeburg in 2001, Bill and Tom Kaulitz met Gustav Schäfer and Georg Listing. Shortly afterwards they founded the band "Devilish" and performed their first regional performances.

In 2003, Bill Kaulitz took part in the "Kinder-Star-Search" talent competition, after which the band was discovered by music producer Peter Hoffmann. In the same year they received their first record contract through Sony BMG under their new band name "Tokio Hotel". Shortly before the release of the first single, Sony BMG canceled the contract, after which the band moved to Universal Music Group for their second contract in 2005. In June 2005, Tokio Hotel celebrated its first TV appearance with Bill Kaulitz as lead singer, Tom Kaulitz as guitarist, Gustav Schäfer on drums and Georg Listing on bass, with their debut single "Über den Monsun". The piece reached number 1 in the German charts in August and Tokio Hotel became one of the most popular German pop bands within a few months. In September 2005, the band released their first album entitled "Schrei", which once again dominated the top spot in the charts in Germany and Austria. In France, "Schrei" reached number 19 in the album charts in the first week, making Tokio Hotel the first German band to enter the French top 20 directly with a debut album.

Meanwhile, in 2005, the musicians, who were still of school age, were awarded the "Bambi" in the "Pop national" category and the "Comet" in the "Best Newcomer" category. In 2006, Tokio Hotel was awarded the "Echo" as "Best Newcomer", the "BRAVO Otto" as "Best Rock Band" and the "Golden Tuning Fork" as "Best German Pop Band", among others. Bill Kaulitz dropped out of school in 2006 in the 10th grade of high school. In the spring of 2008, he and his brother completed their secondary school diploma at an internet school. The twins were awarded the "Distance Learning Youth Prize" in April 2009 for their "exemplary academic achievements". The second album "Zimmer 483" was released on February 23, 2007. Shortly afterwards they were awarded the "MTV Europe Music Award" in the "Inter Act" category. In the same year, 2007, a major European tour followed from March to November. In 2008 they received the "MTV Video Music Award" in the "Best New Artist" category. At the beginning of October 2009, the band's third studio album "Humanoid" was released internationally at the same time for the first time.

In the German version of the animated film "Arthur and the Minimoys" by director Luc Besson, Bill Kaulitz was the dubbing voice of the title hero in 2006 and in the second part (2009). To mark the 30th anniversary of the German edition of "Vogue", Karl Lagerfeld recorded a multi-part photo series with Bill Kaulitz in September 2009. At the 2010 Milan Fashion Week, Kaulitz walked the catwalk as a model for the label "Dsquared2". In the same year, the band received the "NRJ Music Award" in the "Band Of The Year 2009" category and the MTV Europe Music Award in the "Best World Stage Live Performance" category. In 2010, the personal documentary "Through the Night with Wolfgang Joop and Bill Kaulitz" was created in Pars for the TV channel arte. That same year, the twin brothers moved to Los Angeles, where they worked on their fourth studio album. In 2012, Kaulitz and his brother Tom were a jury member for the tenth season of "Deutschland sucht den Superstar".

On October 3, 2014, the band's fourth studio album, "Kings of Suburbia" (Island Records), was released; the first album recorded only in English.