Oswald William Thomas Sidwell (born 16 April 1920) is an Australian former tennis player.
Sidwell reached five Grand Slam doubles finals, winning once, at the 1949 U.S.
National Championships with compatriot John Bromwich.
He also played in the Davis Cup in 1948 and 1949 where Australia lost to the United States both years in the Challenge Round.
As a junior, he won the Australian Open boys' singles event in 1939.
Sidwell is now playing golf regularly in place of tennis.
He was ranked World No.
10 for 1949 by John Olliff.
As of December 2008, Sidwell was still organising golf events at the age of 88.