I disagree with your assessment that far right and populist descriptors are opposites. Admittedly, there's a degree of subjectivity in definitions here, but my understanding is that conventional scholarship has coalesced around a definition of Populism that is agnostic of the left/right spectrum.
For example, this journal article from 2012 defines it as "a thin-centered ideology that considers society to be ultimately separated into two homogeneous and antagonistic groups, the 'pure people' versus the 'corrupt elite', and which argues that politics should be an expression of the general will of the people".
If you care to read a little more, the authors break down their definition into it's constituent pieces and provide context, but the important piece is that you can see how populism can come from both the left and the right.
As examples, we can look at, say, the Occupy Wall Street movement from a while back. Very much spawned from left leaning ideology, but it's defining feature was casting the "corrupt elite" (in this case, the fabulously wealthy) against the general people (i.e. the 99%). On the other side of the coin we can look at Donald Trump's MAGA movement. The image he wants to cultivate is that of an outsider, someone not tainted by the corruption of the Washington elite. That resonates with a sunset of the population.
Both of these movements have radically different goals and politics, but the framework of those arguments follows the same general template.
I apologize for the US-centric examples, but that's what I know. As consolation, the article I linked to is specifically a comparative study of European vs Latin American populism.