The 32-year-old, who previously represented AC Milan, Inter Milan and Udinese in Serie A as well as Portsmouth in England, had been without a club since leaving Saudi Arabian side Ittihad Jeddah at the end of the 2015-16 campaign.
Pescara have gone five games without a victory and languishing at the bottom of the table with nine points after 21 games, twelve points below safety.
"We are happy to announce the signing of Ghana international Sulley Ali Muntari. He will join us until the end of the season and we hope he helps us in our battle to survive relegation," a club statement read.
Muntari is likely to make his debut for Pescara on Wednesday when they host Fiorentina in the league.
He began his career in Ghana with Liberty Professionals before leaving for Europe in 2002, and has earned 84 caps with the Black Stars, boasting of 20 goals.
He last played for Ghana at the 2014 Fifa World Cup in Brazil.