Aaron Bastani, a key supporter of Jeremy Corbyn, blasted the campaign as “absolutely sickening” and called for the Royal British Legion to be shut down in a tirade of online rants.
His comments have been met with huge backlash with calls for him to be axed from the Labour Party.
The owner of left-wing website Novara Media posted the video to the page's 25,000 YouTube subscribers just days before Remembrance Day.
In the video, he says: “We all know about the poppy appeal. It’s something that is a bit of a joke for people on the left.”
He adds: “I feel the poppy appeal is grotesque. I think it has triumphalist militarism to it, which, A, doesn’t really fit with Britain’s military position in the world anymore. And ‘B’, it’s racist, right? It’s white supremacists - I think.”
He goes on to mock a man who built a World War One trench in his garden.
Mr Bastani says: “We’re going to start with a man who has literally reconstructed a World War One trench in his front garden - and it is of course, on a housing estate.
“The only thing that is missing is chlorine gas. What a f****** muppet.”
Not stopping there, he then slammed the Invictus Games, a sporting event for war veterans set up by Prince Harry.
He described the games as “a weird PR exercise for the Royal Family”.
Adding to the onslaught on Twitter, he posted: “Absolutely sickening that as a country Britain spends £45 million on poppies to feel good and help a worthy cause while 13,000 ex veterans are homeless.
“When was the last time the Royal British Legion challenged the government on homelessness and public services? Joke.”
His comments were met with outrage.
Deputy Labour leader Tom Watson responded, saying: “I am proud of our Royal British Legion. They tirelessly work to support our Veterans. This man, who I understand has recently joined the Labour Party, does not speak for it.
“I’m sure all my colleagues will distance themselves from this appalling statement.”
While Labour MP John Mann added: “This ignorant man needs throwing out of the Labour Party today.”
Others responded hastily.
One user said: “Attention seeker, nothing more.”
Another hit out saying: “I will wear my poppy with pride . #Lestweforget”
A third wrote: “Millions died so that Aaron would be free to express his opinions.”
Express.co.uk has contacted the Labour Party for comment.