The winger has signed a four-year deal at the Cardiff City Stadium after agreeing personal terms and passing a medical.
He will wear squad no. 16 and is available for City's home game with Wolves this Sunday, ko 2:00pm.
There are rumours that City are trying to bring West Ham striker Nicky Maynard to CCS.
The transfer window closes tomorrow.
On the departure of Craig Noone Brighton boss Gus Poyet said:
“There can come a time when a club meets our value of a player, the player is willing to go and it is the right move for all concerned.
“That is what has happened with Cardiff and Craig Noone.
“Everything has come together – the price of the player, the player’s decision and the timing.
“We know Nooney is very popular at the club, with the staff, players and fans, and he will be missed.
“Since signing for us from Plymouth, he has been a great guy to have around and a real character – but it is football.
“We thank him for what he has done at this club in the last year and a half, we wish him well and we will be watching out for him.
“I hope he personally does very well with Cardiff.”