The car was the first Brabham to use Alfa Romeo type 115-12 flat 12-cylinder engine with 500 hp (373 kW) and 340 N⋅m (251 lb⋅ft) of torque.

In 1977 Pace finished second in the first race and led for thirteen laps in South Africa with the BT45B, and died a few days later in a plane crash.

His teammate, John Watson, drove to the pole at the Monaco Grand Prix but was passed on the first lap by Jody Scheckter's Wolf, after that he spent more than half of the race in second position, before retiring with gearbox problems.

Jackie Stewart tested an early BT45C (chassis number 8) in 1978 and returned an overall favourable impression of the car as well as the team, with the smooth, torquey Alfa Romeo flat-twelve and the Brabham gearbox coming in for particular praise.

The chassis was not yet fully sorted and Stewart disliked the cable-operated clutch; but the Brabham was still the fastest car he ran in a series of tests at Paul Ricard.