A by-election was held in the state electoral district of Blacktown on 14 October 2017. The by-election was triggered by the resignation of John Robertson (). Robertson served as state Leader of the Opposition from 2011 until 2014.
The by-election was held on the same day as by-elections Cootamundra and Murray.
The candidates in ballot paper order are as follows:
<includeonly> John Robertson () resigned.</includeonly>