Manager Sammy McIlroy told BBC Radio Lancashire: "He's someone I've been after for the last few months. Hopefully he'll tighten us up.
"I've tracked him since his Peterborough days but I didn't have the money to get him. But I'm delighted to have him, he's got good experience."
Charnock, who has featured six times this season for Torquay, returns to Lancashire where had a previous loan spell with Accrington Stanley in 2008/09.
He is in line to make his debut against Crewe on Saturday and will wear the number 27 shirt.
Source: BBC Sport
Source: BBC Sport