The San Siro side have at last completed the signing of the Italy international after protracted negotiations with Sampdoria came to a successful conclusion
The 23-year-old had already been training with Milan since the start of the week, but the transfer had yet to be finalised as both clubs were still in talks over Poland international Salamon.
However, after an agreement was finally reached, Poli has signed a four-year deal with the Rossoneri to wrap up the deal, with the club confirming the news on their official website.
Poli is a product of the Treviso youth academy, but joined Sampdoria at the age of 18. He had since developed into a key player at the Genoa side, making close to 100 official appearances in the past few years.
The Italy international previously wore the jersey of Milan's arch-rivals Inter in 2011-12, but the Nerazzurri opted not to use their option to buy the midfielder after his loan spell.