Born and raised in Surrey, Gethin started his career in sportscar racing, competing in the British Sports Car Championship as a privateer until 1965.

Despite retaining his seat for 1971, Gethin moved to BRM from the Austrian Grand Prix onwards, winning the following race in Italy with an average speed of 242.615 km/h, a record which stood for 32 years.

After competing in the 1974 World Sportscar Championship, driving the Chevron B26, Gethin further finished runner-up in the Canadian-American Challenge Cup and the Rothmans International Series in 1977, before retiring at the end of the season.

The Austrian Grand Prix at the Österreichring was next, and it was another disappointing qualifying session for Gethin, who was down in 21st and comprehensively trounced by his teammates Hulme and de Adamich.

As other drivers fell by the wayside in the race, however, Gethin climbed consistently up the order, and was running as high as 8th before he was passed by Ignazio Giunti's Ferrari and Jo Siffert's March late on, but it was his first grand prix finish as he came home 10th.

Gethin was again the rearmost of the McLaren cars at Monza for the Italian Grand Prix, but it was an improved performance, as he was 17th and as close as he had been to the pole time, 2.050 seconds behind Jacky Ickx's Ferrari.

The Canadian Grand Prix at Mont-Tremblant saw the season leave Europe and head towards its finale in the Americas, and it saw a resurgence in Gethin's form, as he out-qualified both de Adamich and Hulme, coming 11th just 1.7 seconds behind Jackie Stewart's pole time.

It appeared that Gethin's Canada pace had not been carried over, as he was back behind Hulme and in 21st on the grid, 3.05 seconds behind Ickx on pole, although he was ahead of de Adamich.

Tim Schenken and Clay Regazzoni, who was recovering from technical problems, also exposed his deficiencies in racecraft, leaving him 14th and last, and this was where he finished, 8 laps down on winner Emerson Fittipaldi in the Lotus.

He fast dropped behind Hulme and the second Ferrari of Mario Andretti, and when things straightened out he was down in 10th, behind François Cevert's Tyrrell and the Lotus of Emerson Fittipaldi as well.

He won the 1971 Italian Grand Prix with the fastest average speed in Formula One history (until the record was broken by Michael Schumacher in the same race in 2003), but this was his only podium finish.