Elliott officially announced she was running for leadership on February 1, 2018, via Twitter, to replace Patrick Brown who had resigned as leader after sexual misconduct allegations were made against him. Her campaign slogan was "Ready. Now." and her leadership campaign has focused on her experience compared to the other candidates. She stated she supported the "People's Guarantee" (the existing platform adopted by the PC Party in November 2017) with the exception of a carbon tax, which she opposed. She had the most support from the Ontario PC caucus of any leadership candidate in the race. On March 10, she was eliminated on the third and final ballot of the leadership election, which was won by Doug Ford. Elliott had the most votes and had won the most ridings but did not have the most points and therefore came in second. She initially refused to concede to Ford, citing "serious irregularities" in the race and vowed to "investigate the extent of this discrepancy". However, she conceded to Ford the next day and announced her support for him as party leader.
