The BT19 was originally conceived in 1965 as a chassis for a 1.5-litre Coventry Climax FWMW flat-16 engine. Climax abandoned that engine's development before the end of 1965, leaving the single completed BT19 chassis without a power unit and without a race. When the FIA doubled the Formula One engine capacity limit from 1.5 to 3 litres for 1966, a new opportunity arose.
Jack Brabham had persuaded Australian company Repco to develop a new 3-litre V8 engine — lighter and more fuel-efficient than rival Ferrari and Maserati units, if less outright powerful — based on a modified Oldsmobile aluminium block. A disagreement between Brabham and Tauranac over their working arrangement left no time to design a new car, so the unused BT19 chassis was modified to accept the Repco 620 series engine instead. Tauranac described the result as a "lash-up." Brabham called the car his "Old Nail."
Tauranac built the BT19 around a mild steel spaceframe — a deliberately conservative choice when most competitors had moved to monocoques. He judged contemporary monocoques no stiffer than a well-designed spaceframe and harder to repair, a significant concern for a team that also sold customer cars. One distinctive feature was the use of oval-section tubing around the cockpit to stiffen a structurally vulnerable area.
The car weighed approximately 567 kg, some 68 kg above the minimum weight limit but still among the lightest in the 1966 field. Outboard suspension was used all round, again resisting the fashionable inboard configuration — Tauranac's wind-tunnel work had shown inboard suspension offered only a 2% drag improvement, insufficient to justify the extra set-up complexity.
The Repco 620 V8 produced around 300 brake horsepower, well below the 330–360 bhp of Ferrari and Maserati V12 rivals, but its broad torque curve and light weight gave the package superior fuel efficiency — approximately 7 miles per gallon against 4 mpg for the Cooper-Maserati. The BT19 could therefore start a grand prix with only 35 gallons of fuel, around 20 gallons less than heavier rivals. The Hewland HD gearbox initially fitted was later replaced by the sturdier DG unit, which Brabham requested and which subsequently became popular across the Formula One field. For 1967 the car was updated with Repco's new 740 series engine, which featured a redesigned block and centrally mounted exhausts.
The BT19 debuted in the non-championship South African Grand Prix on 1 January 1966, where it took pole position before retiring with a seized fuel injection pump. At the International Trophy at Silverstone it took pole, set a new lap record, and led from start to finish.
The 1966 World Championship season brought four consecutive victories. At the French Grand Prix at Reims, Brabham used the slipstream of Lorenzo Bandini's more powerful Ferrari through the early laps, inherited the lead when Bandini suffered a throttle cable failure, and won — becoming the first man to win a World Championship race in a car bearing his own name. Three more championship wins followed at the British Grand Prix at Brands Hatch, the Dutch Grand Prix at Zandvoort, and the German Grand Prix at the Nürburgring Nordschleife, all in wet or treacherous conditions where the BT19's balance and reliability outweighed its power deficit.
Brabham clinched his third championship at the Italian Grand Prix at Monza, where despite oil pressure failure forcing him out after eight laps, neither rival Surtees nor Stewart finished either.
The BT19 reappeared at three championship races in 1967, debuting the new 740 engine at Monaco and finishing second in the Dutch Grand Prix.
The sole BT19 chassis was retained by Jack Brabham until 1976, when it passed to Repco and was restored. It has appeared at numerous motorsport events since, including the 1985 and 1996 Australian Grands Prix at Adelaide and Melbourne. In 2004 Repco reacquired the car from ACL, and in 2008 it was installed on loan in the Australian National Sports Museum at the Melbourne Cricket Ground.
The BT19 is widely regarded as one of the most significant underdog championship-winning cars in Formula One history. Its 1966 championship demonstrated that a light, reliable, fuel-efficient package could outpoint more powerful but heavier rivals over a full season — a lesson that would be reinforced by many subsequent Brabham and constructors' championship campaigns.