Marcello Di Finzio unfurled a white banner reading "Help us Pope Francis" and called on the Italian government to end harsh austerity measures in the debt-laden country, which is struggling with high unemployment.
"Stop for God's sake, you are killing us all. Give us back our lives," it read.
Di Finzio, who owns a cafe in the northeastern city of Trieste according to Italian media reports, posted a message on Facebook from the dome, saying "they have taken everything from me, but they won't take my dignity as well".
It is Di Finzio's fourth protest on the ledge near the top of the 137-metre (449-foot) dome which was designed by Michelangelo. In a protest last year he stayed up overnight with a banner blaming the Europe Union for the country's ills.
"They lied to me three times, but I won't let them drive me to suicide. If they want to kill me (kill the people) they have to do it in front of everyone, so it's clear these aren't suicides but crimes of state," he wrote.
Suicides linked to the economic crisis make headlines in Italy, where hundreds of thousands of businesses have been forced to close.
Italy returned to growth in the fourth quarter last year after its longest post-war recession, but its jobless rate rose to a record high of 12.9 percent in January, sparking fears that companies are still struggling or unwilling to hire.
The unemployment rate among people between the ages of 15 and 24 rose to a record 42.4 percent.
On Friday, Italy's borrowing costs fell in the latest sign of improved investor confidence in the economy but Italians are still suffering tax hikes and other austerity measures imposed as the eurozone debt crisis gripped the country.
Italian Prime Minister Matteo Renzi, who came to power last month, has promised to reboot the economy by reducing taxes, slashing the costs of Italy's bureaucracy and promoting businesses.