Answer:
In the French legislative Assembly of 1791 and 1792, those members who were conservative and supported the Ancient Regime, sat to the right, while those who were revolutionary, and wanted to create a new social order, sat on the left.
This division was arbitrary at the time, but became the basis of the modern political division that we see today. Conservative parties are said to be right-wing parties, while progressive or revolutionary parties are said to be left-wing parties.