Percy Rees was one of eight children, the son of a cloth merchant, and was educated at Dulwich College. An outside-right, Rees played hockey for Barnes and represented London and The South, winning the first of his 14 international caps against Wales in 1906. Rees and the goalkeeper, Harvey Wood, were the only players to represent England in all their seven matches in the 1908 season. Rees was regarded as the best outside-right until the arrival of Thomas Dashwood in the 1930s.
Rees qualified as an accountant in 1905 and worked in the city. He also worked abroad in The Hague for a while, before taking up the post of sole chief accountant at Unilever in 1931, a post he held until his retirement in 1948. In his work, he was involved with draft recommendations that led to the bringing in of the Companies Act in 1947. During World War I, Rees served as a Captain with the 10th Battalion of the Royal Fusiliers, and won the Military Cross.