He was almost 14 years old in 1984 when he joined New Kids on the Block, a band assembled in Boston by producer Maurice Starr. His fellow members included his brother, Jonathan Knight, as well as Joey McIntyre, Donnie Wahlberg and Danny Wood. Over the next few years he began teaching himself piano, keyboard instruments and writing songs. Starr, who wrote much of the New Kids material, was reluctant to add his work to the band’s repertoire.

New Kids on the Block have sold over 80 million records worldwide, generated hundreds of million of dollars in concert revenues and paved the way for later boy bands like Backstreet Boys and *NSYNC. New Kids on the Block disbanded in 1994, but reunited in 2008.

Knight made a comeback in 1999 by releasing his first solo single, “Give It To You”. The single reached No. 10 on Billboard Hot 100, went gold, and was nominated for the 1999 MTV Video Music Award for Best Dance Video, though it lost to Ricky Martin’s Livin’ La Vida Loca. He was also nominated for Favorite Male Singer at the 2000 Kids’ Choice Awards. The single also peaked at No. 35 on the Hot Dance Music/Club Play chart. The album Jordan Knight won an Aspire Music Award for Best Male Album (Pop). Knight’s self-titled debut album was then certified gold for sales of over 500,000 copies in the US on July 7, 1999. The album peaked at No. 29 on the Billboard 200 and No. 9 on the Top Internet Albums chart. In 2008 the New Kids on the Block reunited and released 2 top 40 hits and went on a successful tour. As of fall 2010, they have teamed up with the Backstreet Boys (BSB), creating the biggest boy band in history, NKOTBSB, and toured in summer 2011.

Knight released a remix album, Jordan Knight Performs New Kids on the Block: The Remix Album, in 2004.

Knight was a judge on the American Idol spin-off, American Juniors. He was a third-season cast member on the VH1 reality television series The Surreal Life with other celebrities in 2004. He later appeared in the 2007 spin-off The Surreal Life: Fame Games, but left during the filming of the premiere episode because of the death of his maternal grandmother.

In 2005, Knight released an EP titled The Fix supported by the lead single “Where Is Your Heart Tonight”, which reached its peak at No. 12 on the Billboard Adult Contemporary chart. He continued to tour extensively in 2005–2006 promoting the EP.

In 2005, Knight appeared on the British show Hit Me Baby One More Time, where he performed “Give It To You”, as well as a cover of “Let Me Love You” by Mario.

In September 2005, Knight also starred in a British documentary on Five in the UK called Trust Me – I’m a Holiday Rep. Six celebrities spent 10 days in the role of an Olympic Holidays holiday rep in Ayia Napa, Cyprus. He initially lacked enthusiasm for the role, which he blamed to some extent on his shyness, but came to enjoy it. In his final debriefing he earned praise from the head reps, who said they would (hypothetically) offer him a job as a children’s and transfer rep.

In September 2006, Knight’s next album, Love Songs, was released by Transcontinental Records. The first single was “Say Goodbye”, a duet with Deborah Gibson, that peaked at No. 24 on the Billboard Adult Contemporary chart.

On May 31, 2011, Knight released his third solo album, Unfinished. The album reached No. 8 on the US Billboard Independent Albums chart, No. 48 on the US Billboard 200 and No. 55 in Canada. He announced began his Live and Unfinished Tour on December 11, 2011. Knight performed the announced dates with Boston-based band Elevation Theory.

Knight also appeared on the game show Identity, hosted by Penn Jillette. In September 2011, he featured as a judge on the CBC show Cover Me Canada.

In 2014, Knight teamed up with Nick Carter for the release of the album Nick & Knight. They are set to tour throughout the fall in support of the album.