Sir Percy Thomas Byrnes (28 January 1893 – 5 March 1973) was an Australian politician.
He was born at Eidsvold in Queensland to water bailiff Thomas Byrnes and Annie Louisa James.
He attended the University of Melbourne, where he received a Bachelor of Science, and served in the AIF during World War I.
He was active in the Country Party, and from 1935 to 1942 served on Swan Hill Shire Council, including a term as president (1939–40).
In 1942 he was elected to the Victorian Legislative Council for North Western Province.