The 19-year-old winger was one of a couple of players Saints were keen to recruit ahead of Thursday's transfer deadline.
The switch to the Clydesdale Bank Premier League outfit has been confirmed by the Swans.
A statement on the Barclays Premier League club's website read: "Young Swans winger Gwion Edwards has joined St Johnstone on loan in the Clydesdale Bank Premier League.
"Edwards, 19, will spend the rest of the season on loan at McDiarmid Park under the managerial guidance of Steve Lomas, who gave lengthy service to Man City and West Ham as a player, before coaching spells at Norwich and a return to the Hammers as a reserve team boss.
"The local Lampeter-product signed for the Swans' Under-15s squad before rising through the ranks to become an important part of the successful FAW Welsh Youth Cup campaign in 2010.
"He signed his first pro-contract the following summer and was set to make his first-team debut off the bench in added-on time in the final league game against Liverpool last season, but he didn't make it onto the pitch before the final whistle blew."
The Perth club are also in talks with Newcastle over a loan move for Abeid Mehdi.
- Sports & Recreation
- Clydesdale Bank Premier League
- Barclays Premier League