Feilding was born on 2 August 1943 in Mere, Wiltshire, the son of William Feilding, 10th Earl of Denbigh, and Verena Barbara (née Price). He was the only son in the family and was educated at Eton College. On 2 September 1965 he married Caroline Judith Vivienne Cooke, daughter of Lt.-Col. Geoffrey Cooke, in London. The couple had three children: Lady Samantha Clare (born 1966), Lady Louisa Helen (born 1969), and Alexander Steven Rudolph (born 1970), who later succeeded as 12th Earl of Denbigh and 11th Earl of Desmond. Feilding inherited the earldoms of Denbigh and Desmond from his father on 31 December 1966, at the age of 23.
The Earldom of Denbigh dates from 1622, created for William Feilding, 1st Earl of Denbigh, a prominent courtier and naval officer. The family seat was Newnham Paddox in Monks Kirby, Warwickshire, a historic house associated with the Feildings since the fifteenth century.
Feilding entered his first motor race in 1964 at the Autosport Silverstone meeting, driving a Lotus Seven and finishing sixth in the S/GT2.0 class. Later that year he raced a Ferrari 250 GTO (chassis 4399GT) for the BRSCC at Mallory Park, finishing second overall and first in the GT+2.5 category — a strong result in a car that remained one of the most coveted GT racing machines of the era.
In 1965 he expanded his programme, entering European Formula Three in a Cooper T76-BMC alongside sports car events. At the 1000 km of Nürburgring he shared a Ferrari 250 GTO with Peter Clarke but retired on the opening lap. He also raced at the 12 Hours of Reims with Clarke, retiring early with starter motor failure.
The 1966 season was his most substantial. In the BRSCC Les Leston Formula Three Championship he drove a Brabham BT18-Ford for the George A. H. Drummond Racing Organisation and finished eighth in the standings, with a race victory at Snetterton on 25 September 1966. He also entered international Formula Three events that year, finishing sixth at the Grand Prix des Frontières at Chimay, fourth at the Circuito Internacional de Vila Real in Portugal, and seventh at the Grande Prémio de Portugal at Cascais. His best sportscar result of 1966 came at the Rand Daily Mail Nine Hour Endurance Race at Kyalami, where he and Peter Clarke shared a Ferrari 275LM and finished second overall and first in class — a result that demonstrated his capability in serious GT competition at an international level.
In 1967 Feilding continued in the RAC Sportscar Championship with a 3.3-litre Ferrari 275LM and returned to Chimay, finishing sixth in a Brabham BT21-Ford for Michael Pearson Racing. In 1968 he attempted to enter the 24 Hours of Le Mans sharing Alain de Cadenet's Sodec-Diva Martin Valkyrie with co-driver Tommy Weber, but the entry was not accepted by the organisers. He retired from active racing at that point, having competed for five seasons across Formula Three, GT, and prototype categories.
After leaving motorsport, Feilding became a dealer in Rolls-Royce and other luxury sports cars. In the 1970s he moved into advertising, working as an executive in London. He also managed rock bands during this period, among them The Animals during their later years — a combination of interests that placed him at the intersection of 1960s British counter-culture and the entertainment business.
Feilding maintained a lifelong passion for motorcycling, undertaking extensive journeys across the world and keeping a cherished Ducati at Newnham Paddox. He died on 23 March 1995 in Newnham, Hampshire, at the age of 51. His estate was valued at £1,417,775. He was succeeded in both earldoms by his son Alexander.