List of United Kingdom MPs with the shortest service

This is an annotated list of the members of the United Kingdom Parliament since 1900 having total service of less than 365 days.

Nominal service is the number of days that elapsed between the declaration (or deemed election) and the date of death, defeat, disqualification, resignation or other cause of termination.

Effective service is the number of days elapsed between taking the oath as a member of Parliament (if the member did so) and the date of death, resignation, disqualification or dissolution of Parliament. In other words, this number is the maximum number of days the member could have sat in Parliament, whether or not they actually did so.

This list includes Irish Republican MPs who were elected but did not serve in the House of Commons due to their abstentionist policy.