Facing the biggest test of his career, the Welshman was on top from start to finish to comfortably retain his belt.
Challenger Braithwaite, who was put down in the fifth, did well to go the distance as he took some heavy punishment.
However, Maccarinelli had to settle for a point success, the judges scoring it 120-107, 118-109 and 119-108 in his favour.
The duo certainly entertained the crowd, standing toe-to-toe in the centre of the ring and trading blows.
Braithwaite is well known for his punching power yet it was Maccarinelli who looked the stronger of the two as he unloaded some big shots.
Victory extends his professional record to 27-1 and he is likely to fight next on the undercard of Joe Calzaghe's fight with Mikkel Kessler in November.
Alex Arthur was in action on the undercard in the Welsh capital, the Scot producing a stunning stoppage of Kobo Goboladze.
The 29-year-old floored his opponent three times before the referee eventually stepped in to save the American in the 10th round.
Arthur is now the mandatory challenger for Joan Guzman's world title, although the champion is expected to move up in weight.
However, the performance of the night came from Gareth Rees, as he claimed the WBA light-welterweight title with a stunning display against Souleymane M'Baye.
Rees, who was banned for a year back in 2004, made the most of a fast start to build up a healthy cushion.
Although he had to weather a late storm the 27-year-old hung on to clinch an amazing win and become Wales' 10th world champion.
