Noone, 24, has become Malky Mackay's ninth signing of the summer for a fee believed to be £1m.
The Liverpool-born wideman started his career at Plymouth Argyle before joining the Seagulls for £300,000 in January 2011.
Noone, who has scored 11 goals in 60 appearances for Brighton, Exeter and Plymouth, is expected to make his debut at home to Wolves on Sunday.
Cardiff have already signed Craig Bellamy,Tommy Smith,Heidar Helguson,Matthew Connolly,Joe Lewis,Jordan Mutch,Kim Bo-Kyung, and Etien Velikonja this summer.
Cardiff City have signed Brighton winger Craig Noone on a four-year deal.