Larry Brock Becomes Seventh MP to Leave Poilievre’s Caucus Since Election; Four Crossed to Liberals

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Larry Brock built much of his political identity around the courtroom, and that is where he now intends to return. The Ontario Conservative announced on August 6 that he will resign as MP for Brantford—Brant South—Six Nations effective September 18 and resume work as a Crown prosecutor in Brantford. The Canadian Press counts Brock as the seventh MP to leave, or announce a departure from, Pierre Poilievre’s Conservative caucus since the 2025 election, including four MPs who crossed directly to Mark Carney’s Liberals. Brock’s case is different: he is not switching parties and has expressed confidence that Conservatives will retain his riding. Still, his planned exit adds another vacancy to a period of unusually visible Conservative caucus turnover and puts fresh attention on what each departure means for Poilievre, Carney and the balance of power in Parliament.

Brock Is Trading Parliament for the Courtroom

Brock’s departure has a personal logic that distinguishes it from the four Conservative defections that preceded it. Before entering federal politics, he spent almost 19 years as a prosecutor. He was first elected to Parliament in 2021 and later became one of the Conservatives’ most recognizable voices on criminal justice, bail and public safety. Brock served as the party’s justice critic before leaving that role during Poilievre’s June 2026 shadow-cabinet changes. His parliamentary interventions repeatedly drew on his experience inside courtrooms, making criminal justice less of a secondary portfolio than a defining part of his political profile.

That background also explains the language Brock used when announcing his September 18 resignation. He said he wanted to return to the “front lines of justice” at the Crown attorney’s office in Brantford and stressed that his commitment to community safety had not changed. Poilievre publicly thanked him for his work on bail, victims’ issues and public safety. There was no announcement of a party switch or rupture with Conservative policy. In fact, Brock said he had confidence that the community would be represented by another Conservative. The immediate story, therefore, is not a defection. It is a prominent justice-focused MP deciding that his next chapter belongs back inside the legal system rather than on Parliament Hill.

The “Seventh Departure” Comes With an Important Counting Detail

The Canadian Press described Brock as the seventh MP to leave Poilievre’s caucus since the 2025 election, with four of those MPs crossing to the Liberals. That tally is most clearly understood as the four floor-crossers — Chris d’Entremont, Michael Ma, Matt Jeneroux and Marilyn Gladu — plus Richard Martel, Cathay Wagantall and Brock. Martel has already left the House, while Wagantall has announced an August 31 resignation and Brock’s takes effect September 18. In other words, some of the seven are completed departures and others are scheduled ones.

There is another wrinkle for anyone checking the official House of Commons ledger. It also records Conservative Damien Kurek resigning on June 17, 2025. His case, however, was an unusual tactical handoff: Kurek vacated the exceptionally safe Battle River—Crowfoot seat specifically so Poilievre could contest a by-election after losing Carleton in the general election. Poilievre subsequently won that August 18 by-election and returned to the Commons. That makes Kurek’s resignation politically different from an MP abandoning the Conservative caucus or leaving for another career. The distinction explains why a simple count of every Conservative resignation recorded by Parliament does not neatly match the current Canadian Press description of the caucus churn surrounding Poilievre.

Four Conservatives Made the Bigger Move — Joining Carney

The most politically consequential departures were the four MPs who did not leave Parliament at all. Chris d’Entremont became the first of the group on November 4, 2025, leaving the Conservatives for the Liberals after saying Carney’s budget better reflected priorities he had heard in his Nova Scotia riding. Michael Ma of Markham—Unionville followed on December 11. Ma framed his decision around national unity and what he called Carney’s steady, practical approach on affordability, economic growth, community safety and opportunities for families. Both moves mattered because Carney was governing without a majority and every additional Liberal seat changed the parliamentary arithmetic.

Matt Jeneroux produced an even more unusual turn on February 18, 2026. The Edmonton Riverbend MP had previously announced plans to leave the House, but instead remained in Parliament and joined the Liberals, becoming the third Conservative defector. Carney also gave him a special-adviser role focused on economic and security partnerships. Then came Marilyn Gladu on April 8. The longtime Sarnia-area Conservative became the fourth Conservative MP to cross, saying uncertainty created by American tariffs required serious leadership and arguing that Carney offered a plan for a stronger, more self-reliant Canada. Four different ridings and four individual explanations ultimately produced the same parliamentary result: seats elected under the Conservative banner moved directly onto the government benches.

Martel and Wagantall Show Why the Other Exits Are Different

Richard Martel’s July departure did not strengthen the Liberal caucus directly. The Chicoutimi—Le Fjord Conservative resigned from the Commons after Carney selected him for the Senate. Martel had represented the Quebec riding since 2018 and held several opposition responsibilities over his federal career. His appointment created a vacancy rather than transferring a Commons vote from one party to another. At the time, Canadian Press coverage described him as the fifth Conservative MP to leave the opposition benches since the 2025 election, after the four floor-crossers. Poilievre’s reaction was notably different from his criticism of the defectors: he congratulated Martel and said he hoped the former MP would continue advancing Conservative priorities in the upper chamber.

Cathay Wagantall represents another category entirely. The Saskatchewan MP announced in June that she would resign Yorkton—Melville effective August 31 after representing the riding since 2015. She did not provide a reason for changing earlier plans to remain through the next election, but she explicitly affirmed support for Poilievre and said she believed he would become prime minister. Taken together, Martel, Wagantall and Brock demonstrate why caucus attrition should not automatically be treated as seven identical votes of no confidence in the leader. Four MPs joined Carney. One moved to the Senate. Two announced departures from elected politics while maintaining support for the Conservatives.

Conservatives Begin With a Strong Base in Brock’s Riding

Brock’s resignation nevertheless creates a real electoral test because another by-election will eventually have to be held. The starting numbers favour the Conservatives. In the April 28, 2025 general election, Brock received 34,501 votes in Brantford—Brant South—Six Nations, or 52.4 per cent of valid ballots. Liberal candidate Joy O’Donnell finished second with 27,032 votes, or 41.1 per cent. That gave Brock a margin of 7,469 votes and 11.3 percentage points. It was a comfortable victory rather than a photo finish, although the Liberal share was substantial enough to ensure the coming contest will attract national attention.

There is also a longer Conservative history behind those numbers. Canadian Press reporting notes that the area has been represented federally by Conservatives since 2008, when Conservative Phil McColeman defeated Liberal incumbent Lloyd St. Amand. Brock therefore leaves his party with an established local organization and a recent majority of the vote, not a seat won narrowly in a one-off upset. A by-election can still behave very differently from a general election, especially without an incumbent on the ballot. That is what makes the coming race useful for both major parties: Conservatives will want to demonstrate that Brock’s support belonged largely to the party, while Liberals will have an opportunity to test whether Carney’s national gains can reach into another southwestern Ontario Conservative seat.

Brock’s Vacancy Arrives During an Already Busy By-Election Period

The timing makes Brock’s decision more significant than a single resignation might otherwise appear. Three federal by-elections are already scheduled for August 31 in Beaches—East York, Ontario; Chicoutimi—Le Fjord, Quebec; and North Vancouver—Capilano, British Columbia. Those vacancies were created by the departures of Liberal MPs Nathaniel Erskine-Smith and Jonathan Wilkinson and Conservative Richard Martel. The Liberals need to win at least one of the three contests to preserve majority control in the Commons. On that same August 31 date, Wagantall is scheduled to leave her Saskatchewan seat, creating another vacancy that will eventually require voters to return to the polls.

Brock’s resignation follows only 18 days later, on September 18. The House of Commons calendar has the chamber returning for its fall sitting on September 21, meaning Brock intends to leave just before MPs reconvene in Ottawa. His riding will not immediately vote on a replacement: federal law provides a window for calling a by-election after the Speaker formally notifies the chief electoral officer of a vacancy. Elections Canada says the writ must be issued between the 11th and 180th day after receipt of that warrant, with the campaign itself lasting no more than 51 days. The result is an autumn in which candidate recruitment, local campaigns and parliamentary seat counts will remain moving pieces rather than settled questions.

Poilievre Faces Bad Optics, but the Leadership Picture Is More Complicated

Seven departures or announced departures create an obvious political communications problem for any opposition leader, particularly when four MPs have moved directly into the governing party. Every defection gives Liberals an opportunity to portray Carney’s coalition as expanding and Conservatives an incentive to argue that voters, rather than MPs, should decide when partisan allegiance changes. Yet caucus turnover alone does not show that Poilievre has lost his party. At the Conservative convention in Calgary at the end of January, he received 87.4 per cent support in his mandatory leadership review — an overwhelming endorsement from participating party delegates only months before Brock’s announcement.

Carney, meanwhile, has converted opposition defections and by-election victories into something tangible. The Liberals reached 174 seats in the 343-seat House after winning three April 13 by-elections, transforming the minority elected in 2025 into a parliamentary majority. Later resignations narrowed that cushion, which is why the August 31 contests matter again. Brock will not be contributing another seat directly to Carney, and his stated confidence in a future Conservative MP makes his case fundamentally different from the four crossovers. Even so, politics is shaped partly by accumulation. One departure can look personal; repeated departures become a storyline. Poilievre now has to contain that storyline while proving that Conservative voters, candidates and remaining MPs are still firmly aligned behind a party that intends to replace Carney’s government.

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