The Google HTTPS ranking algorithm, which launched some time ago, hasn't proven to many webmasters and SEOs as being all that significant. With that being said, one webmaster asked Google's Gary Illyes about that on Twitter.
Gary Illyes responded on Twitter saying it acts as a dealbreaker when two sites are in a tie for the same number one ranking.
Gary Illyes wrote in response to being asked how much does HTTPS play a role in Google's rankings, it is "more like a dealbreaker. All other signals being more or less equal, it gives a page the edge needed to top the other result."
Here is the tweet:
@MattSouthern more like a dealbreaker. All other signals being more or less equal, it gives a page the edge needed to top the other result— Gary Illyes (@methode) July 21, 2015
Gary said this before, as covered by Jennifer Slegg out of the SMX Sydney coverage.
Forum discussion at Twitter.