West dropped the bombshell after admitting that he had smoked a "little something" before getting up on stage.
He then droppd the microphone and ran off stage.
The last word was left to MTV host Miley Cyrus: "Now we all know what happens to Kanye West when he smokes weed," Cyrus said.
The award was presented to West by Taylor Swift - who he famously interrupted on stage at the VMAs in 2009 - and he covered a variety of topics in his speech.
"I will die for the art, for what I believe in, and art ain't always going to be polite," he said.
"We gotta teach our kids that they can be something. That they can stand up for themselves. If my grandfather was here, he would not let me back down."
The Michael Jackson Vanguard Award is presented to artists who have made a profound effect on MTV culture, honouring their body of work over time.
This isn't the first time the outspoken Chicago rapper has dabbled in talk of politics.
West is noted for criticism of President George W Bush and the federal government's response after Hurricane Katrina.
He has also compared the world's fascination with his wife Kim Kardashian to that of the first lady.
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- AP with nzherald.co.nz
