The Chinese Super League has a reputation for quick turnaround of managers.
Poyet, 49, was himself sacked earlier this month by struggling Spanish outfit Real Betis.
Shenhua announced that the one-time Real Zaragoza, Chelsea and Tottenham midfielder arrived in the Chinese commercial hub on Tuesday and would begin training the team later this week.
Shenhua's performance last season earned them a berth in the AFC Champions League but the club terminated Manzano's contract earlier this month, citing unspecified "considerations about the team's future strategic development and in order to achieve its objectives for the new season".
A club announcement said it expects Poyet to "further improve on the team's tactics and put in an outstanding performance in both Asian and domestic matches in the new season."
The Chinese Super League has a reputation for quick turnaround of managers. Besides Manzano, former England coach Sven-Goran Eriksson was let go from Shanghai SIPG this month.
In 2012, Guangzhou Evergrande replaced Lee Jang-Soo with Marcello Lippi mid-season after the Korean coach had taken them to promotion and the CSL title in consecutive years.
Evergrande also moved swiftly to replace Lippi's eventual successor, Fabio Cannavaro, with Luiz Felipe Scolari after the Italian had guided them to the top of the table last year.