She was a Progressive Conservative member in the Legislative Assembly of Ontario from 2006 to 2015. She represented the ridings of Whitby—Ajax and Whitby—Oshawa, east of Toronto. Elliott was a candidate in the 2009 Progressive Conservative leadership election and came in third place behind winner Tim Hudak and runner-up Frank Klees. She was appointed as the party's deputy leader in 2009. She was a candidate for 2015 leadership election but lost to former federal MP Patrick Brown. Following her second loss, Elliott resigned her seat in the legislature and was appointed as Ontario's first Patient Ombudsman by then-Ontario Minister of Health and Long-Term Care Eric Hoskins, serving until she stepped down to make her third bid for the Ontario PC Party leadership. In that contest, Elliott won the most votes and ridings but lost the contest to Doug Ford. She then received the nomination to run for the riding of Newmarket-Aurora and was elected on June 7, 2018, as the PC Party won the election.