A tumultuous close-season saw adored head coach Antonio Conte surprisingly leave the Turin club, having guided Juve to three successive Scudetti.
Conte has since taken the Italy job, paving the way for Allegri - whose four-year spell at Milan ended in January - to take the reins.
The 47-year-old's tenure will begin at Stadio Marc'Antonio Bentegodi this weekend in the opening game of the 2014-15 season, with big-money striker Alvaro Morata and former Manchester United defender Patrice Evra both poised to make their debuts.
Allegri's former club, Milan, will also be led by a new coach as Filippo Inzaghi takes charge for the first time against Lazio on Sunday.
Inzaghi was appointed to replace the sacked Clarence Seedorf, who filled in at the end of last season following Allegri's departure, and will be desperate to get off to a winning start.
Like Juve, Inter are likely to give a former United stalwart his first Serie A outing as high-profile recruit Nemanja Vidic is set to start at Torino.
Inter will be targeting a good beginning to a crucial campaign as they attempt to challenge Juve and Roma for the title following a fifth-placed finish last term. A Champions League return is also in Inter's sights.
Last year's runners-up have a trio of new faces at their disposal in Ashley Cole, Juan Iturbe and Kostas Manolas.
Elsewhere, Atalanta take on Verona and Sassuolo tackle Cagliari.
