On 18 January 2017, O'Leary officially entered the Conservative leadership race. That same day, his former Dragons' Den co-star Arlene Dickinson stated that she found O'Leary to be too "self-interested and opportunistic" to be qualified for the office of prime minister. In response, another former Dragons' Den co-star, W. Brett Wilson, endorsed O'Leary, highlighting differences between O'Leary as a businessman and his TV persona.
On 1 February 2017, O'Leary posted a video of himself shooting in a Miami gun range. It was removed from Facebook out of respect for the funeral for three victims of the Quebec City mosque shooting on that day. It was also revealed that he was in New York promoting one of his business ventures when this occurred. O'Leary later apologized for the timing of this post.
O'Leary was a frontrunner in the polls throughout most of his run. Nevertheless, he dropped out of the leadership race on 26 April 2017, stating that, though he still thought he could win the leadership election, a lack of support for him in Quebec meant that it would be difficult for him to beat Trudeau in 2019, and that it would thus be "selfish" of him to continue. On dropping out, he endorsed Bernier, considered the other main frontrunner for the position. (Andrew Scheer eventually won the leadership election, narrowly edging out Bernier.)
In a 2017 interview with Evan Solomon, O'Leary suggested that Senators should pay money every year, instead of being paid, thus turning "a cost centre to Canada" into "a profit centre."