A man who once scaled the CN Tower in Toronto to unveil a banner that called Canada and former U.S. president George W. Bush "climate killers" is now entering federal politics as a star candidate for Prime Minister Justin Trudeau's Liberals.

Steven Guilbeault, a star Quebec environmentalist, is scheduled on Friday to announce his plans to seek the Liberal nomination in a Montreal riding, Laurier-Ste-Marie, that was once held by former Bloc Québécois leader Gilles Duceppe.

The move could boost Trudeau's credentials in Quebec at a time when many environmentalists are disappointed in the government's decision to spend billions of dollars of public money to assume responsibility for the Trans Mountain pipeline expansion and the subsequent reapproval of the project, which would increase capacity by three times.

The announcement comes nearly 18 years after Guilbeault climbed up the CN tower to unveil the "climate killers" banner, protesting former prime minister Jean Chrétien’s and Bush's stance on the Kyoto Protocol. At that time, Guilbeault was an activist for Greenpeace. He and fellow activist Christopher Holden later pleaded guilty to public mischief and paid a fine to cover the security costs prompted by the protest.

Under Chrétien, Canada would later ratify the Kyoto climate agreement, to date the only international agreement that set binding commitments on developed countries, in 2002. But Canada would unilaterally withdraw from the agreement under former prime minister Stephen Harper in December 2011.

Guilbeault has said he is motivated to stop Andrew Scheer's Conservatives, currently leading in public opinion polls, from forming a government.

Scheer introduced a 60-page environmental policy platform this week that commits to meeting Canada's new international commitments under the Paris Agreement. But the Conservative plan does not elaborate on how its proposals could realistically achieve those targets.

One of the best known figures on Quebec's environmental stage due to his work with Équiterre and Greenpeace Quebec, Guilbeault has been nicknamed the "Green Jesus of Montreal" by La Presse. On the international stage, French newspaper Le Monde listed him among the world’s 50 leading actors in the field of sustainable development in 2009.

He was among a small group of activists who founded Équiterre in 1993, eventually turning it into one of Quebec's most prominent conservation groups that now counts 22,000 members, 200 volunteers and 50 employees. Their organization has consistently been on the front lines of activism shaping public policy. Most recently, it is known for efforts to crack down on harmful pesticides such as neonicotinoids and promote action on climate change, including recent battles to electrify the province's transportation network and to stop the proposed Energy East pipeline, a project that was eventually abandoned in 2017 by Calgary-based energy company, TransCanada Corp.

Most recently, Guilbeault has co-chaired a panel advising the federal government on climate change policies and has appeared frequently in recent months at events with the prime minister and other members of cabinet.

The Laurier-Ste-Marie riding is now held by NDP MP Hélène Laverdière, who defeated ex-Bloc Quebecois leader Gilles Duceppe in 2011 and again in 2015. She announced in July 2018 that she wouldn't be running again in 2019.