Merzario made his Formula One debut in 1972, and became one of the few drivers to score points at their first race by finishing in sixth place in the British Grand Prix at Brands Hatch. In 1973 Ferrari confirmed him for the whole season alongside Jacky Ickx. Merzario had a promising start with the old 312B2, finishing fourth in Brazil and South Africa. However, Ferrari's evolved car, the 312B3, proved to be a disappointment, and both he and Ickx struggled for the rest of the season. Deeply unimpressed with the way the season had unfolded, Enzo Ferrari decided to change the whole team for the 1974 season, and Merzario moved to Williams. After finishing third in a non-Championship race in Brazil, Merzario scored points at the Monza and in South Africa. However, the Williams cars were largely uncompetitive, and in 1975, after a one-off with the Copersucar at Monza, where he finished eleventh, Merzario returned to sports cars with Alfa Romeo — winning four races plus the Targa Florio again.