The popular 29-year-old has signed an initial one-year deal following his departure from National League rivals Hartlepool United.
Sloggett enjoyed a hugely successful loan spell with the Pilgrims in March and April - establishing himself as a key cog in United's survival mission.
He made nine appearances in total - including six from the start.
Sloggett linked up with his team-mates on Monday morning - and could feature in the Pilgrims' opening pre-season friendly against Lincoln United on Saturday.