During the First World War Birkin entered the Royal Air Corps where he contracted malaria, an illness that was to affect him throughout his life.

Birkin was part of the celebrated group of drivers tagged the 'Bentley Boys'. He started racing at Brooklands in 1921, but, owing to family commitments, he had to interrupt his career and it wasn't until 1927 that he raced again.

In 1928 Birkin upped the power of his engine and opted for the 4.5 litre, in which he performed well. His wins led to the decision to turn professional, against the wishes of his family. He did so well that he led for 20 laps at Le Mans in 1928 before mechanical problems slowed him down and saw him slip to fifth. At the end of the 1930s the 'Bentley Boys' broke up and Birkin bought himself a Maserati 8C-3000 and an Alfa Romeo. Birkin used the Alfa in Sport races and the Maserati for Grand Prix, in which he claimed a third spot in Tripoli in 1933.

It was this very race that was claim to Birkin's life. During a pit stop in his Maserati, Birkin had accidentally placed his arm on the exhaust pipe, burning it. The wound did not seem too serious at first, so much so that Birkin did not consider medical attention necessary. When he returned to England a few days later though, he realised that the injury had worsened - partly due to the malaria he had contracted in wartime. The wound had turned septic and three weeks later Birkin passed away in a London hospital.