The 20-year-old, who resides in Louth, has agreed a two-year contract at the Jakemans Community Stadium.
Grist, who progressed through Grimsby Town’s youth system prior to linking up with Leicester, will add defensive depth for Graham Coughlan’s squad.
He spent the second half of the 2024-2025 campaign on loan with Northern Premier League play-off winners Worksop Town.
Grist will officially link up with the Pilgrims on July 1 upon the expiry of his contract at King Power Stadium.