Not all earthquakes that ever happened have been recorded. We've only recorded them for a little over a century, I believe. So you can't tell for certain. But the biggest earthquake on record is the Valdivia earthquake, from 1960. It measured 9.5 on the Richter scale. (a scale ranging from 1-10)
The highest magnitude earthquake occurred in Chile in 1960 with a scale of 9.5.