Big Bang at MTV Fast Forward, Thailand, December 2007
Prior to his involvement with YG Entertainment, Seung-hyun was an underground rapper under the name of Tempo, and a childhood friend of G-Dragon, another member and leader of Big Bang. G-Dragon stated that the two were "neighborhood friend[s] from middle school" and would often dance and rap together. Although G-Dragon later moved away and the two "became distant", he contacted Seunghyun again when YG Entertainment was scouting for candidates to create a boy band. The pair recorded several demos and sent them to Yang Hyun Suk, CEO of YG Entertainment, who later asked Seunghyun to audition. Seunghyun was initially rejected by the record label, which deemed him too "chubby" to fit the "idealistic version" of an idol. Seunghyun later stated that he "went home and exercised really hard because I wanted to join YG Entertainment." Six months later, he returned for another audition and was signed on. He reportedly lost 20 kg in 40 days. Choi Seung-hyun was given the stage name of T.O.P. (Korean: 탑) by fellow YG artist Se7en. He became one of the two rappers in the group Big Bang, alongside G-Dragon. The two were paired with four others: Taeyang, Daesung, Seungri and Jang Hyun-seung and a documentation of their training was aired to promote them. So-1 was dropped by the record label, and Big Bang made its official debut with five members. Their first album, Since 2007, was a fair success, and included T.O.P.'s first solo song "Big Boy." The group achieved mainstream success with the release of the song "Lies" (Korean: 거짓말; Revised Romanization: Geojitmal) from their 2007 mini-album Always, which topped several charts upon its release. The singles, "Last Farewell" (Korean: 마지막 인사; Revised Romanization: Majimak Insa) from the mini-album Hot Issue and "Day by Day" (Korean: 하루하루; Revised Romanization: Haru Haru) from Stand Up, became chart-toppers as well.
2007–10: Solo career development, move into acting, and GD&TOP
Following the release of the band's albums and singles, T.O.P. began working on his solo career. In April 2007, he was featured with fellow Big Bang members Taeyang and G-Dragon on singer Lexy's single "Super Fly" for her album Rush. Later that summer, he appeared as an actor in Red Roc’s "Hello" music video. He later became the first member of Big Bang to venture into acting, starring in the KBS2 drama, I Am Sam,. portraying the school's top fighter, Chae Musin. He also took the role of MC of MBC's Music Core on November 10, 2007, only to resign in April of the following year. In 2008, he collaborated with R&B artist Gummy on the song "I'm Sorry" for her album Comfort, veteran singer Uhm Jung-hwa for her single "D.I.S.C.O." and ZiA for her single "I Only See You". That same year, he was also admitted to Dankook University, to the theater department.
T.O.P later put his solo career on hold while he joined Big Bang for their promotional activities. After more than a year of promoting the group's materials, he returned to acting, playing the assassin Vick in the critically acclaimed Korean television drama Iris. T.O.P. also recorded the song "Hallelujah" for the drama's soundtrack with Taeyang and G-Dragon. Following Iris, T.O.P. and his fellow Bigbang member, Seungri appeared in the teenage suspense drama, 19 which they released a song titled "Because".
GD & TOP promotional photo shoot
His appearance in the 2010 film 71: Into the Fire was well-received, earning him several awards including the Hallyu Popularity Award in the 47th Grand Bell Film Awards. The movie also gained 1 million views in a week, making it the first movie of 2010 to do so South Korea. Simultaneously, T.O.P began to prepare for his solo musical debut. During Big Bang's Big Show concert in January 2010, T.O.P. performed his new single "Turn It Up." They later uploaded an official video, which garnered over a million views within a few minutes. He became the first Korean artist to have his song released worldwide on iTunes.
In November 2010, YG Entertainment announced T.O.P and bandmate G-Dragon would release a collaboration album under the name "GD&T.O.P". Preceding the release of the album, the duo held a world-wide premiere showcase for their album at Times Square in Yeongdeungpo of Seoul, South Korea, which was also broadcast live on YouTube. To promote their album, the duo released three singles: "High High," "Oh Yeah," and "Knock out." All three singles preceded the release of the album. The singles attained commercial successes: "Knockout" was a chart topper while "Oh Yeah" and "HighHigh" both peaked at #2 and #3 respectively. The album was released on Christmas Eve, and debuted at number one with pre-orders of 200,000 copies.
During 2011, Big Bang halted their activities following the release of their Tonight extended play because of Daesung's car accident & G-Dragon's marijuana scandal. He attended 2011 MTV EMAs with his group Big Bang, which they won the category for Best Worldwide Act.
In 2012, T.O.P starred in the film Commitment (also known as Alumni), playing the son of a North Korean spy who is falsely accused. During filming a combat scene for the movie, he injured the back of his hand on a glass fragment and was later admitted to the hospital for surgery. Filming of the movie was delayed for several weeks, though despite his injury he continued to appear with Big Bang throughout their world tour. For his role, he won Rookie Award at the Asia Star Awards, held during the Busan International Film Festival, the only Korean actor who won an award in the ceremony.
T.O.P was named one of the hottest sex symbols in 2013. In November, he released a digital single, "Doom Dada"  which he himself regarded it as strange and weird. It was his latest single after 3 years with the release of "Turn It Up" in 2010. The song was performed for the first time at the Mnet Asian Music Awards 2013 in Hong Kong  He was later featured in English artist Pixie Lott's Japanese album along with G-Dragon for the song "Dancing On My Own". In 2014, T.O.P portrayed the role of main character Ham Dae-Gil in the South Korean gambling film Tazza 2: The Hidden Card, sequel to Tazza: The High Rollers.
After debuting as a furniture designer in 2015 in collaboration with Vitra, he was awarded the Visual Culture Award at the Prudential Eye Awards.