A member of the Hammersmith SC, Percy Peter came second in the one mile National Championship at the age of 18 and his performance earned him selection for the Great Britain Olympic team. It was to be the first of three Olympics he took part in from 1920-28 but his bronze with the 4 x 200 m freestyle relay in 1920 was to be his only medal. In 1928 Peter made an Olympic appearance as a water polo player. He was a well-known long-distance swimmer, winning the British Championships in the River Thames swims in 1922, 1924 and 1929.
In 1921 Peter moved to the famous Penguin SC and was the Southern Counties one mile champion 1921-23 he was runner-up in the ASA mile championship in each of those years to Jack Hatfield. He was the 440y National Champion in 1923 and after several runners-up positions in the half-mile championship, eventually won the title in 1927. Peter was also the National Salt-Water 440y champion 1921-23 and in 1924 and 1925 was a member of the Penguin Club that reached the final of the National Team Championships. Apart from his three Olympic appearances, Peter swam for the British Empire against the USA at Harrow shortly after the 1924 Olympics, was capped for England at water polo, and took part in the 400 m freestyle and water polo events at the 1927 European Championships.