Maddock was born in Sutton, Surrey, in January 1925, the son of architect Richard Maddock. He studied engineering at Kingston Technical College while serving in the local Home Guard during the latter years of the Second World War. After two years of National Service in Germany he returned to Kingston for a refresher course, and sought practical workshop experience among the cluster of small automobile manufacturers based in Surrey at the time — including AC, Alta, and HWM.
Beyond engineering, Maddock was an accomplished jazz musician. He played trombone, saxophone, bass clarinet, piano, and sousaphone, and performed with several bands of the late 1940s and early 1950s including Mick Mulligan's Magnolia Jazz Band, where vocalist George Melly remembered him as a towering, bearded figure whose clothes were perpetually streaked with oil. When the Magnolia Jazz Band turned fully professional Maddock chose to remain an amateur and left the group.
Maddock joined the Cooper Car Company in September 1948, initially filling roles as draughtsman, fitter, storekeeper, and van driver. He quickly became known as "The Beard" around the works — Charles Cooper privately called him "Whiskers" — for his distinctive full beard, unusual in the racing paddocks of that era. His talent for lateral thinking and the artistry of his technical drawings earned him growing responsibility in the design process, which became a three-way collaboration between Maddock, John Cooper, and star driver Jack Brabham.
In 1953 Maddock introduced two design features that became Cooper hallmarks: the curved-tube chassis frame and the "curly leaf" leaf-spring location bracket, both debuted on the Mark VIII Cooper 500 Formula Three car. The curved-tube concept broke orthodox space-frame engineering rules but allowed bodywork to be attached directly to the frame, saving weight and complexity. It remained a Cooper signature despite vocal criticism from Brabham.
Maddock's first bespoke Formula One design came not for Cooper but for industrialist Tony Vandervell: the Vanwall Special (Cooper T30) of 1953–54, a front-engined car whose taut chassis drew praise from test driver Alan Brown. Vandervell went on to win the inaugural World Constructors' Championship in 1958 with extensively revised Vanwall cars, but by that point the mid-engined Cooper revolution Maddock was engineering was about to overtake the field.
The Cooper T39 sportscar of the mid-1950s — nicknamed "Bob-tail" for its abbreviated Kamm-tail bodywork — provided the evolutionary stepping stone to Cooper's first Formula One challenger. Jack Brabham persuaded the Coopers to build a Formula One variant around a Bristol engine; subsequent development proved the rear-engined layout competitive and pointed the way forward.
Maddock's Cooper T41 (1956) and T43 (1957) established the mid-engined template at the highest level. On New Year's Day 1958, Stirling Moss drove Rob Walker's modified T43 to victory in the Argentine Grand Prix — the first World Championship win for a rear-engined car, achieved against full-capacity 2.5-litre rivals. The follow-on T45 continued the breakthrough: Maurice Trintignant won the 1958 Monaco Grand Prix in Walker's entry, and the works cars scored additional points.
The Cooper T51 of 1959 represented the maturation of Maddock's design. Jack Brabham and Bruce McLaren took three victories and eight podiums between them across nine championship rounds; additional wins from Moss and Trintignant in customer T51s completed an emphatic title sweep. Cooper took the World Constructors' Championship and Brabham the Drivers' title — the first time a mid-engined car had achieved either feat in Formula One. Brabham retained the Drivers' title in 1960 with the refined T53.
The 1961 engine regulations — cutting the maximum displacement from 2.5 litres to 1.5 litres — required a fundamental rethink of chassis design. Cooper struggled to match the nimbleness of Lotus and BRM under the new formula. Brabham left to found his own team after 1961, removing a critical design contributor. McLaren's 1962 Monaco Grand Prix win in the Cooper T60 proved to be the works team's last victory under original ownership.
Maddock began developing a monocoque chassis using aviation-grade aluminium honeycomb sandwich construction — a technically advanced concept that anticipated the composite monocoques that would later become universal. Limited finances and manufacturing complexity led Cooper to abandon the project; Maddock noted that the same structural principle would not win the World Championship until the Williams FW07 of 1980. Feeling trapped and wanting new challenges, Maddock resigned in August 1963.
Maddock joined Saunders-Roe on the Isle of Wight, drawn by the company's hovercraft development programme, and settled in Cowes for the remainder of his life. After Saunders-Roe was merged into the British Hovercraft Corporation he continued in the field until industry contraction led to redundancy. In December 1963 he had written a letter to Flight International's Air-Cushion Vehicles supplement seeking fellow enthusiasts for racing hovercraft; the response led to the formation of the Isle of Wight Hover Club in 1964 and the national Hovercraft Club of Great Britain in 1966, of which Maddock was a co-founder and long-serving technical secretary.
In parallel, Maddock contributed freelance engineering work to Bruce McLaren Motor Racing, including significant input on the McLaren M1A sportscar of 1964. His design for McLaren's four-spoke cast racing wheel proved exceptionally stiff and became a hallmark of McLaren competition cars across many series through the 1970s. He later consulted for March Engineering, who offered him a full-time position he declined in favour of remaining independent.
Owen Maddock's work at Cooper defined the mid-engined revolution in Formula One. The T51's 1959 championship demonstrated conclusively that mounting the engine behind the driver — a layout Cooper and Maddock had refined from motorcycle-engined 500 cc club racing machines — was the path all serious Formula One constructors would follow. Within two years every competitive Grand Prix car had adopted the configuration. Maddock remained active as a musician and amateur sportsman until shortly before his death in Cowes on 19 July 2000.