In 2011, MacLaren contested the party's nomination in the riding of
Carleton—Mississippi Mills competing against the sitting MPP
Norm Sterling, who had represented the riding and its predecessors in Queen's Park for 34 years. In the
2011 provincial election, MacLaren defeated
Liberal candidate Megan Cornell by about 9,102 votes. In the
40th Parliament of Ontario, MacLaren served as his party's deputy critic for infrastructure and transportation from October 26, 2011, to September 30, 2013, when he was promoted to be his party's critic for Senate and Democratic reform. On July 4, 2014, it was announced that MacLaren would continue to be the party's critic for Senate and Democratic Reform. In November 2014, MacLaren introduced a
private member's bill to repeal the law that grants environmental protections for the
Niagara Escarpment for the second time. MacLaren was the second MPP to back former federal Conservative
Patrick Brown's successful bid for leadership in the
2015 Progressive Conservative leadership election, bringing with him the supporter of the small but dedicated Ontario Landowners Association In June 2015, MacLaren was accused of betraying social conservative values by Nick Vandergragt, a conservative radio talk show host on Ottawa's
CFRA for marching in that year's
Toronto Pride parade alongside PC leader
Patrick Brown and other conservatives, both federal and provincial. MacLaren was named his party's Critic for Natural Resources and Forestry on September 10, 2015, as well as the vice-chair of the relevant committee. Brown also made MacLaren, a
libertarian, the chairman of the PC's
Blue Ribbon Panel on Property Rights. On November 26, 2015, MacLaren officially invited a "group of friends and guests" from the Tamil community to hear him make a speech in Queen's Park about the "genocidal onslaught for the Tamils" in Sri Lanka. The
Toronto Star reported on March 3, 2016, that MacLaren had been making inquiries on behalf of challengers to MacLeod in her
Nepean—Carleton riding. MacLaren refused to comment and the Progressive Conservatives dismissed the claims in the story. At the Ottawa party convention which was ongoing when the story broke, Brown publicly endorsed MacLeod's renomination as candidate.
Leave, demotion, and sensitivity training MacLaren was forced to apologize on April 6, 2016, after calling his federal Liberal counterpart
Karen McCrimmon to the stage at a cancer fundraising dinner the previous month in
Carp, and then telling a vulgar joke about her and her husband's sexual relationship. MacLaren emailed an apology to McCrimmon after the story was first reported by the
Toronto Star. On April 12, 2016, the
Ottawa Citizen reported that MacLaren's website included a testimonials section praising his work where most of the constituents were fictional and were represented by photos that had been taken without permission from the internet. One of the testimonials was from a "Robert & Karen" from
Constance Bay, which coincidentally is where MacLaren's federal counterpart, Liberal MP Karen McCrimmon lives with her husband Robert. MacLaren then issued an apology for the improper use of constituent testimonials and had his website taken offline. MacLaren kept his position as the shadow cabinet critic for natural resources, the chair of a party panel on property rights, and as an ambassador to ethnic communities. On May 31, 2016, MacLaren returned to Queen's Park after completing his sensitivity training.
Expulsion from PCs, first Trillium Party MPP On May 28, 2017, Brown expelled MacLaren from the PC caucus, purportedly after a video recording surfaced of a 2012 speech in which he criticized French language rights in the province, and indicated that the party would act to limit them once in office. Brown also stated that MacLaren would not be allowed to run as a Tory in the next election. After his expulsion was announced, he released a statement on Twitter saying he had joined the
Trillium Party of Ontario. Brown said that while there had been rumours of MacLaren leaving to potentially form his own party, Brown personally was unaware of MacLaren's plan to join the Trillium Party until after he found out about the video and expelled him. In an interview with
Evan Solomon on
CFRA after his expulsion, MacLaren said that he had grown unhappy with the direction that Brown was taking the party and hadn't spoken to him in a year. MacLaren said that he felt he could serve his constituents better with the Trillium Party, and that the Progressive Conservatives had no values and its establishment was anti-democratic. He also characterized Solomon's questions on the reasoning for his dismissal as "talking about something that isn't helping anybody" and a valueless waste of time. Since the Trillium Party lacked
official party status in the
Legislative Assembly of Ontario, MacLaren was officially counted as an independent. In the
2018 election, he lost his bid for re-election in the new riding of
Kanata—Carleton, essentially the Ottawa portion of his old riding. He finished fifth out of seven candidates after losing over half of his vote from 2014. == Electoral record ==