Tom was born on September 1, 1989 in Leipzig , Saxony , Germany at 06:20 am. He has a twin brother, Bill Kaulitz . Their parents, Jörg and Simone, separated when they were 7 years old. Simone married years later, with Gordon Trümper, guitarist of the German band Fantun. Bill 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 band. According to Bill in several interviews, he and Tom started writing music at seven. Their friends Georg Listing (Bass guitar) and Gustav Schäfer (Drummer).

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 Tom. The group, founded in 2001, changed its name to Tokio Hotel after signing with Sony in 2003.

In 2005, they released their first album " Schrei ", with the first single " Durch den Monsun ", which was very successful in Germany, and they toured throughout the country throughout that year. In 2007, they released their second album, " Zimmer 483 ", and to promote it they went on tour again, but this time throughout Europe. Because of the huge number of fans around the world, they decided to re-record the songs "Schrei" and "Zimmer 483", but this time in English, the result being the hugely successful album " Scream) ", from which their most powerful song so far was released, " Monsoon ". They went on tour for the third time, but this time, they also included America. In 2009, they released their second studio album in English and their third in German, Humanoid, and to promote it they went on tour for the fourth time. After 5 years of inactivity in the music scene, together with Tokio Hotel, they decided to launch Kings of Suburbia and in 2017 Dream Machine. Then they released 2001 in 2022.

On August 4, 2010, Tom Kaulitz got his own Reebok shoes commercial. Reebok signed the 20-year-old Tokio Hotel guitarist and sneaker addict to model shoes for the company. “At home, I created a little room, like a little storage room,” he said of his sneakers. He also said that he gets 10 new pairs a week.

Tom and Bill released an app named “BTK Twins” for Android on December 19, 2011, and on iOS on January 16, 2012, to keep in touch with their fans[source?]. On the app, Tom and Bill posted photos, videos, and text messages, and fans could leave messages which the twins often respond to. In November 2013, the app was removed from both the Android and IOS stores, due to the imminent release of Tokio Hotel’s new album.

Tom, like his brother Bill, is a staunch defender of animal rights and welfare . He has collaborated with PETA on two campaigns, one against the mistreatment of animals in zoos and circuses and the other against the killing of stray animals in Ukraine. Most of his pets have been adopted from shelters. He has also helped raise funds for the fight against AIDS.

Tom was known for his style and hairstyle. He wore baggy clothes, a cap, a lip piercing, and dreadlocks or braids. He speaks 3 languages: German, English, and French. He got his first guitar from his stepfather when he was nine years old. He owns 17 guitars and 50+ caps. Once when he was on tour he had an entire luggage just for his caps.

Tom and Bill used to live in Hamburg but moved to Los Angeles in October 2010 in response to an incident involving stalkers and a robbery. They are currently living in Los Angeles making music.

Tom dated the German model Ria Sommerfeld from 2011 to 2016. They were married for over a year, until Tom filed for divorce citing irreconcilable differences in September 2016. Tom also dated the German model Mai Schiller from December 2017 to March 2018. Tom is now married to German-American model and television host Heidi Klum since 2019.