The 1923 Portsmouth South by-election was a parliamentary by-election held in England on 13 August 1923 to elect a new Member of Parliament (MP) for the UK House of Commons constituency of Portsmouth South in Hampshire.
The seat had become vacant when the constituency's Conservative MP Leslie Orme Wilson had been appointed as Governor of Bombay, and had therefore resigned from the Commons on 26 July by the procedural device of accepting appointment as Steward of the Manor of Northstead. Wilson had held the seat for less than a year, having won it at a by-election in December 1922. He had previously been the MP for Reading from 1913 to 1922.
The result at the last election was:
Cayzer was re-elected for Portsmouth South at the next five general elections, and held the seat until he was ennobled in 1939. Lawson never stood for Parliament again. The result at the following general election;