Jay Kay was born in Stretford, Greater Manchester, on 30 December 1969. His mother, Karen Kay, is a former cabaret singer and television personality. His biological father is Luís Saraiva, a Portuguese former guitarist, whom he did not meet until 2001. Kay's identical twin, David, died some weeks after they were born. Kay said in a 2010 interview with The Daily Telegraph that his mother raised him largely alone, which gave him "an itinerant childhood; half of it living in rural Suffolk and rural Devon". A 1997 article in the Lancashire Evening Telegraph states that Kay "moved with his mother and step-father Mervyn Kay to Manchester as a youngster". He attended Oakham School in Rutland. At 15 years old, Kay was homeless and turned to small crimes to survive. He soon returned to his home after a false arrest and a near death experience. From there, he pursued a career in music and worked as a regular in night clubs. Prior to forming his own band, it was widely reported that Kay failed an audition to become a singer of the Brand New Heavies. The group however, denied these claims.
Kay formed Jamiroquai in 1992. Band members include Toby Smith (keyboards), Stuart Zender (bass), Nick Van Gelder (drums, 1992–1993), Derrick McKenzie (drums 1994–present) and Wallis Buchanan (didgeridoo). After the success of Jamiroquai's first single, When You Gonna Learn, Kay signed a US$1 million record deal with Sony Soho2. The band's first album was Emergency on Planet Earth. The relationship with Sony ended in 2007. The band has sold more than 26 million albums worldwide. Kay is occasionally referred to as 'Jamiroquai', due to the misconception that the band is actually a solo artist.
Kay is well known for his array of elaborate hats and headgear. Professional appearances for concerts, interviews and the like have prompted descriptions of Kay as "the mad hatter" for his love of headgear. In 2005 it was announced that Kay, often referred to as "the cat in the hat", was launching a range of distinctive clothing, including his trademark hats, on his new "Quai" label. The Indian Country Media Network has criticised him for wearing sacred regalia of the First Nations.
Kay appeared in an episode of the BBC series The Naked Chef alongside chef Jamie Oliver. He has also performed on the series Strictly Come Dancing singing "Canned Heat". He also appeared four times in the BBC car show Top Gear. The first appearance was in series 1, episode 2, where he set a lap time of 1:48.1 for the show's "Star in a reasonably priced car", becoming (and remaining) the person with the fastest lap time for the rest of the first series and most of the next series. His second appearance was in series 3, episode 4, where Kay drove his Lamborghini Miura with Richard Hammond as a passenger. The third appearance was in series 11, episode 6, where he beat the top time held by Simon Cowell by one-tenth of a second.  He succeeded with a lap time of 1:45.8. Kay won Top Gear's "John Sergeant Award" for the best dance after learning that his time on the Top Gear test track was the fastest lap time in 2008.
In a 2010 interview, Kay stated that he at one point had "substantial" cocaine habit. He has been free of drugs since 2003.