The 1858 Wairarapa and Hawke's Bay by-election was a by-election held in the Wairarapa and Hawke's Bay electorate during the 2nd New Zealand Parliament, on 22 July 1858.

The by-election was caused by the resignation of incumbent MP J. Valentine Smith and was won unopposed by James Ferguson.^[1] Owing to an arbitrary shortening of the time between the issue of the writ and the holding of nominations at Castlepoint (where a single nomination was received) the election was over before many electors knew it was due to take place. Charles Carter had published his intention to stand on 17 July – five days before the nomination.^[2] The validity of the election was called into question^[3] and a petition was sent to the Governor requesting a new writ,^[4] although it seems it was disallowed. The Electoral Districts Act 1858 (coincidentally passed a few weeks after the election)^[5] split the electorate in two with Ferguson declared as incumbent in County of Hawke and Carter winning Wairarapa in the 1859 supplementary election.