Puafisi arrives in the West Country following the conclusion of his country's autumn tour, in which he started their last outing against Wales at the Millennium Stadium on Friday.
His most recent club contributions have come in New Zealand with the Tasman Makos, with whom he tasted ITM Cup glory this season.
"Sila's arrival will allow our front row options to be deeper and also create competition in that position, which can only be a good thing going forward," said Gloucester director of rugby Nigel Davies, who already has fellow Tongans Lua Lokotui and Sione Kalamafoni in his ranks.
"It's taken quite a lot of work, the work behind the scenes in these cases can often be quite lengthy. But he's been in fine form in the ITM Cup and for Tonga, and I'm confident that we have added a quality player to the squad.
"Having Lua and Sione here already has been a big help. Sila has been able to find out more about Gloucester from them and, in turn, they've confirmed that we've got the right man."
Puafisi made his Tongan Test bow in 2011, having previously represented his country at U18, U19 and A level, and, as well as starting the 17-7 defeat in Cardiff, was a replacement against both Romania and France earlier this month.
His addition to the Gloucester squad comes after the Cherry and Whites lost full back Olly Morgan to retirement and allowed centre Tim Molenaar to join Harlequins, developments which freed up Davies to amend his group as he saw fit.