The Primeira Liga champion has reinforced its squad by investing the financial windfall earned from the big-money sales of Joao Moutinho and James Rodriguez.
The Dragoes paid out 8 million euros for an 80 percent share of the highly-rated prospect, who won an Olympic gold medal at the 2012 Games with the Mexico Under-23 side.
Herrera, who has gone on to become a senior Mexico international since, signed a contract binding him to the club for the next four seasons, with a buyout clause set at 40m euros.
"I have fulfilled a dream in coming to a big club in Europe," the 23-year-old confirmed to Porto's official website. "I've always had this goal and Porto gave me this opportunity. Now I want to start working as soon as possible to show why they signed me and believed in me.
"I consider myself a dynamic midfielder, always on the move and seeking the ball. I turn up in attack frequently and know how to create chances."
He is the Estadio do Dragao side's second purchase ahead of the 2013-14 campaign, given Diego Reyes - fellow Mexico international had been snapped up on pre-contract agreement in December 2012.
Incoming coach Paulo Fonseca will see Herrera as a direct replacement for the departed Joao Moutinho after the latter was sold to Ligue 1 spender Monaco for 25m euros in May.