The following table contains the by-elections that have occurred during the term of the 15th Parliament.
| Electorate and by-election | Date | Incumbent | Cause | Winner | |||
|---|---|---|---|---|---|---|---|
| Pahiatua | 1904 | 28 July | John O'Meara | Death | Bill Hawkins | ||
| City of Wellington | 1905 | 6 April | George Fisher | Death | Frank Fisher | ||