The Seahawks signed Duplessis on Wednesday, Ari Horton of the team's official site reports.
The Seahawks invited Duplessis to a tryout Wednesday and signed him on the same day, with the Delaware product taking the spot vacated by Kenny McIntosh, who was waived by Seattle on Monday. Duplessis logged 60 catches for 824 yards and five touchdowns across 13 games in his final collegiate season, but he's considered a long shot to make the Seahawks' 53-man roster at the end of training camp.