It was a rebellion against the established order (the monarchy) to form the first liberal democratic state (based on a slave economy). The dynamics weren't dissimilar to socialist revolutions in the following centuries, just now the established order is the liberal democracies that the monarchies transitioned into (either peacefully or through violent insurrection).

So not at all leftist as we mean today, but leftist in the sense that they were against the monarchy which I believe was the initial use of the term in France? Supporters of the status quo stood on the right and the supporters of the transition to liberal democracy stood on the left.