He accused chief electoral officer Marc Mayrand of opposing the controversial, proposed overhaul of elections laws because he wants more power for himself, more money and less accountability.
Moreover, Poilievre said Mayrand is making "astounding," "amazing" and untrue allegations as he grasps at straws to defeat Bill C-23, the so-called Fair Elections Act.
"His recommendations really boil down to three broad requirements for him," Poilievre told the Senate legal and constitutional affairs committee as it launched a "pre-study" of the bill before the House of Commons considers amendments or passes it.
"He wants more power, a bigger budget and less accountability."
The broadside drew sharp condemnation in the Commons during the daily question period.
"Will the prime minister stand in this House and apologize to parliamentarians, and apologize to Marc Mayrand, for that cowardly, baseless attack on Canada's chief electoral officer?" NDP Leader Tom Mulcair demanded.
Stephen Harper responded by congratulating Philippe Couillard, the Quebec Liberal party leader, for his victory Monday night in the provincial election.
Liberal MP Kevin Lamoureux, who sits on the Commons committee studying the bill, said it was "shameful" that Poilievre would "verbally assault" the chief electoral officer.
"I stand by my testimony from this morning at the Senate committee," Poilievre cooly responded.
For his part, Mayrand refused to respond in kind. At an appearance before the same Senate committee later Tuesday, he once again dissected the bill and pointed to five "deeply concerning provisions."
"My role is to point out to Parliament some issues that may arise from any legislation that governs elections," he said later outside the committee.
"I think that's my duty, my responsibility and I'm trying to fulfil it to the best of my abilities."
One of Mayrand's biggest concerns is that up to 120,000 voters could be disenfranchised if, as proposed, individuals are no longer allowed to vouch for voters who don't have proper documentation proving their identity or address.
Only three provinces and the federal government require voters to prove not just their identity but that they live in the polling district in which they want to vote, Mayrand told the committee. Proof of address is problematic for students, seniors in long-term care facilities, those living on aboriginal reserves and transients.
As a result, he said all four jurisdictions allow vouching as a "failsafe" mechanism so that those who can't prove residency don't lose their constitutionally guaranteed right to vote.
Outside committee, Mayrand said proof of residency is almost "unique" to Canada. It is not required in Britain, Australia, India or the United States, except for one state.
Poilievre told senators he is "at peace with" Mayrand's objections to the bill but disagrees with his recommendations.
And he reminded the committee that the chief electoral officer is supposed to serve Parliament, "not the other way around."
Among the "new powers (Mayrand) seeks for himself," Poilievre cited the recommendation that Elections Canada be empowered to audit the books of political parties and demand invoices and receipts — a long-standing request by Mayrand and his predecessor, Jean-Pierre Kingsley.
He argued it's sufficient that parties must hire an external auditor to verify their election expense returns.
He dismissed another long-standing request that the elections commissioner, who investigates breaches and enforces election laws, be empowered to seek a court order to compel witness testimony. Poilievre said not even the police have such powers, yet they still secure convictions.
"If Elections Canada can not do the same, perhaps that says something about the cases being investigated, rather than the powers of the investigator."
Elections commissioner Yves Cote has said the inability to compel witnesses has frustrated his ability to investigate the robocall scandal, in which thousands of primarily non-Conservative voters in 2011 received misleading calls directing them to the wrong polling stations. A Federal Court judge has concluded the calls were made using the Conservative party's massive voter identification data base.
Poilievre reserved his most scathing criticism for Mayrand's opposition to the proposal to move the elections commissioner out of Elections Canada and put it under the auspices of the director of public prosecution.
"He is fighting to retain this power, making some incredible claims and inventing some novel legal principles to do it," he asserted.
Mayrand has actually been relatively muted on this issue.
Both elections commissioner Cote and his predecessor, William Corbett, last week argued that housing the investigative and prosecutorial functions in the DPP's office departs from the long-standing principle of keeping the two functions separate — "a separation that was deemed sufficiently important in 2006 to remove prosecutions from the commissioner," Cote noted.
Poilievre said it's "astounding" to claim there's some "ancient principle" of separation between the investigative and prosecutorial functions when it comes to election laws. Prior to the creation of the DPP seven years ago, he noted that the elections commissioner was responsible for both investigating and prosecuting breaches of the law from within Elections Canada.
"With these arguments, one is left with the perception that the CEO is grasping to find some justification to remain in charge of the investigator."
A Commons committee is simultaneously conducting hearings on the bill and has yet to consider any possible amendments.