Boris Bondarev, 41, confirmed his resignation in a letter delivered on Monday morning at the Russian diplomatic mission after a diplomatic official passed on his English-language statement to the Associated Press.
"For twenty years of my diplomatic career I have seen different turns of our foreign policy but never have I been so ashamed of my country as on February 24 of this year," he wrote, alluding to the date of Russia's invasion.
Reached by phone, Bondarev - a diplomatic counsellor who has focused on Russia's role in the Conference on Disarmament in Geneva after postings in places like Cambodia and Mongolia - confirmed he handed in his resignation in a letter addressed to ambassador Gennady Gatilov.
The resignation amounts to a rare - if not unprecedented - public admission of disgruntlement about Russia's war in Ukraine among the Russian diplomatic corps, at a time when Putin's government has sought to crack down on dissent over the invasion and sought to quell conflicting narratives from the government line about how the "special military operation" is proceeding.
"It is intolerable what my government is doing now," Bondarev told the AP.
"As a civil servant, I have to carry a share of responsibility for that, and I don't want to do that."
Bondarev said he had not received any reaction yet from Russian officials but added: "Am I concerned about the possible reaction from Moscow? I have to be concerned about it."
Asked if some colleagues felt the same, he added: "Not all Russian diplomats are warmongering. They are reasonable but they have to keep their mouths shut."
He suggested his case could become an example.
"If my case is prosecuted, then if other people want to follow, they would not," he suggested.
In his English-language statement, which he said he emailed to about 40 diplomats and others, Bondarev said those who conceived the war "want only one thing - to remain in power forever, live in pompous tasteless palaces, sail on yachts comparable in tonnage and cost to the entire Russian Navy, enjoying unlimited power and complete impunity."
He railed against the growing "lies and unprofessionalism" in the Russian Foreign Ministry and took particular aim at Foreign Minister Sergey Lavrov, who he said in "18 years, he went from a professional and educated intellectual… to a person who constantly broadcasts conflicting statements and threatens the world (that is, Russia too) with nuclear weapons!".
"Today, the Ministry of Foreign Affairs is not about diplomacy. It is all about warmongering, lies and hatred."
Bondarev told the AP that he had no plans to leave Geneva.
Hiller Neuer, executive director of the advocacy group UN Watch, said: "Boris Bondarev is a hero."
"Bondarev should be invited to speak in Davos this week," he added, "and the US, the UK and the EU should lead the free world in creating a program to encourage more Russian diplomats to follow and defect, by providing protection, financial security and resettlement for diplomats and their families."
