[5] He was sired by the Grand Prix de Saint-Cloud winner Sea Hawk, from whom he inherited his colour, out of Bombazine, a mare who had finished fourth in The Oaks.
[4] In April 1975, Bruni finished second in a maiden race oven one mile at Sandown Park and then won a similar event at Salisbury in early May.
Bruni entered contention for the Epsom Derby when he was moved up in distance to 1+1⁄2 miles and finished second, beaten a short-head, to No Alimony in the Predominate Stakes at Goodwood.
[8] Bruni's progress persuaded Lester Piggott to choose him as his ride in the Derby but he started an outsider at odds of 16/1 in a field of eighteen runners.
Ridden by Tony Murray and starting at odds of 9/1, Bruni took the lead early in the straight and drew steadily clear of his opponents to win by ten lengths from King Pellinore and Libra's Rib.
He began his season in the Yorkshire Cup at York Racecourse in May and won easily while carrying the "top weight" of 127 pounds, beating Mr Bigmore and Sea Anchor by two lengths.
[11] After his poor performance in the previous year's Derby, Bruni bypassed the Coronation Cup at Epsom and was sent to Royal Ascot for the Hardwicke Stakes.
[13] Bruni was unplaced in all of his three starts while in the United States, with his best effort being a fifth-place finish in the 1977 San Luis Rey Handicap at Santa Anita.
[4][13] Bruni contested the two and a half-mile Gold Cup at Royal Ascot, but made no impression in the straight and finished fourth to Sagaro, Buckskin and Citoyen.
[4] In July he was dropped in distance for a second attempt at the King George VI and Queen Elizabeth Stakes and finished seventh of the eleven runners behind The Minstrel and Orange Bay.