The Nottingham Forest defender scored the only goal of Sunday's Championship game in first-half injury time, as the East Midlands side registered their second victory of the campaign.
The win keeps Argyle, who now have to travel to Peterborough United on Tuesday, pinned to the bottom of the table, five points from safety.
The only goal of the game came in time added on to the additional minute's injury originally added by referee Andy Woolmer.
Gunter exchanged passes with former Argyle loan player Dexter Blackstock and benefited from a slip by substitute James Chester to fire home with his left foot.
Chester, on loan from Manchester United, fell in front of Gunter and, although he still managed to get his head on the ball from his prone position, could not prevent the Forest man from finishing.
The goal seemed to knock the stuffing out of the home side, who had wasted a glorious chance to open the scoring in the opening exchanges when Jamie Mackie could only steer Gary Sawyer's driven cross wide from a decent position.
A little later, Mackie made room for himself on the left and fired off a shot that Forest keeper Lee Camp just managed to keep out, despite being wrong-footed.
The second half saw Forest make plenty of headway against an Argyle team whose weakened defence saw them fielding two on-loan teenage centre-backs against the wily Blackstock and Dele Adebola.
Chester, on the pitch because of a hamstring tear to Icelandic international Kari Arnason, and Aston Villa defender Shane Lowry had their hands full but eventually came through well and Argyle keeper Romain Larrieu barely had a shot to save.
However, at the other end, Argyle were similarly bereft of creation, with only a long-range shot from another substitute, Alan Judge, causing Camp any concern.