Radium was foaled in 1903 at Southcourt in Leighton Buzzard, the stud of his breeder and owner Leopold de Rothschild.

His dam, Taia, was also bred by Rothschild and was a half-sister to the horse Eros (winner of Althorp Stakes).

After a place in a race at the Goodwood meeting, Radium won the Prince of Wales's Nursery Stakes at Doncaster.

[8] Returning as a three-year-old, he was third to Beppo and Bridge of Canny in the Union Jack Stakes in Liverpool and was unplaced for the Newmarket Biennial.

Radium's only Classic race start was in the 1906 Derby, which was won by Spearmint, where he battled with Troutbeck for a fourth-place finish.

Following uncontested wins in the Rous Stakes and Rutland Handicap, Radium defeated the 11-4 favorite The White Knight in the Ascot Gold Cup.