The 26-year-old winger, who can also play at left-back, has agreed a four-year contract at the San Siro.
The Nerazzurri made no secret of their pursuit of the Uruguay international, confirming their approach with an interview posted on their offical website on Friday.
And a statement released on inter.it this evening read: "Alvaro Pereira is officially an Inter player.
"The relevant documents have been lodged with the Serie A for the permanent transfer of the Uruguayan player from Porto.
"Pereira has signed a four-year contract."
After joining the Dragoes from Cluj in 2009, Pereira was part of Andre Villas-Boas' Europa League winning team in 2011, also claiming two Portuguese league championships and six domestic cups.
Pereira links up with countrymen Fredy Guarin and Walter Gargano in Inter boss Andrea Stramaccioni's new-look squad.