"When I undertook the task of Independent Special Rapporteur on Foreign Interference, my objective was to help build trust in our democratic institutions. I have concluded that, given the highly partisan atmosphere around my appointment and work, my leadership has had the opposite effect," Johnston said in a letter to Prime Minister Justin Trudeau.
"I am therefore tendering my resignation, effective no later than the end June 2023, or as soon as I deliver a brief final report, which I hope to be earlier."
This move comes after the embattled former governor general testified before MPs this week, appearing insistent in his plans to forge ahead with public hearings next month.
In the meeting, Johnston called the allegations swirling around his objectivity "quite simply false."
Trudeau appointed Johnston to the role in March, as part of a suite of measures responding to concerns the Liberal government failed to share information, or respond adequately to the threat of foreign interference in the last two federal elections.
From the outset of his appointment, the former governor general has faced consistent personal and partisan attacks from opposition parties, accusing him of bias despite a lengthy career of appointments to non-partisan roles by political leaders across the spectrum.
In his interim report released May 23, while pointing to the real threat that foreign election interference poses and the need to address some serious intelligence gaps, Johnston recommended against a public inquiry, but announced plans of his own to conduct public hearings.
This prompted a new wave of fury, with the opposition calling it the latest example of how Johnston has a conflict of interest, an assertion Johnston repeatedly denied on Tuesday.
"I don't believe I have a conflict of interest and I would not have undertaken this responsibility, had I had a conflict of interest," he said.
Last week, the majority of MPs in the House of Commons passed an NDP motion calling for him to "step aside" as rapporteur, calling for Johnston to remove himself from the role as rapporteur given the "serious questions" raised.
In response, Johnston dismissed this call and made it clear he plans to stick around, saying that while he "deeply" respects the right of the House of Commons to "express its opinion about my work going forward" his mandate is from the government and he feels that he has a "duty to pursue that work until my mandate is completed."