Van Dongen, the party's only sitting MLA, says he can't continue in the party while it's led by John Cummins.
"I want to emphasize I came to the party in good faith," he told reporters.
"But I cannot carry on with a leader who probably really doesn’t care whether I stay or go, and so I’ve got to do what I believe is right for my constituents and what I believe is right for British Columbians."
Van Dongen, who bolted from the governing Liberals to the Conservatives, says he will sit as an Independent in the legislature.
Hours earlier, party members voted 70 per cent against holding a leadership review.
A group of party members led by vice-president Ben Besler had been seeking to oust Cummins as party leader.
The group, which calls itself Friends of B.C. Conservative Party, is running a seven-member slate for the party's executive positions.
The most recent poll by Angus Reid put the Conservatives in third place with 19 per cent voter support, behind the governing Liberals at 25 per cent and the opposition NDP at 46 per cent.
Also on HuffPost