The 19-year-old made a blistering impact in last year's FFA Cup after joining the Mariners in mid-2019.
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Silvera's impact led to a trial with MLS powerhouse LAFC in January but the starlet returned from the United States without securing a deal.
Silvera ended the season having made 21 appearances for the Mariners, who finished last for the fourth time in the past five A-League campaigns.
His match-winning strike against the Glory was his only goal for Alen Stajcic's team.
"It feels amazing to be moving to Europe. I feel like the football in Portugal will suit my style and I will be working hard to succeed over there," Silvera said.
"Over this past year I feel as though I've grown and developed so much as a footballer and I can't wait to take this next step forward in my career."
Pacos de Ferreira, who finished 13th in last season's Primeira Liga, kick-off their 2020-21 season on Sept. 21.