In a recent Vox article, the author claims (without citation):
In 1820, some 94 percent of humans lived on less than $2 a day. Over the next two centuries, extreme poverty fell dramatically; in 2018, the World Bank estimated that 8.6 percent of people lived on less than $1.90 a day
However, I am afraid he did not adjust for inflation as this seems a frighteningly common problem with news media. Adjusting for inflation, $2 would represent ~$50 in modern purchasing power (About 7% of humans lived on > $50/day in 2011 according to Pew).
I cannot find world-wide wage information for 1820 to check this $2 figure however.