From Cory Doctorow (edited)

"Populism" isn't intrinsically left or right. There's a simple litmus test : "ask what's more important: human rights, or property rights. If they say 'property rights are human rights,' they're on the right."

Both the left and the right can be populist, but the populist left seeks to improve peoples' lives, no matter what that takes, the populist right is only willing to make the world better when that doesn't interfere with the interests of property owners.