Josh Key put pen to paper on a three-year contract, which includes the option for an additional 12 months, in the summer on 2023.
The 23-year-old joined the Swans after spending the previous eight years on the books at Exeter City.
Key, who can play as a full-back, wing-back or winger, became the first players to join the Swans from Exeter since captain Matt Grimes in 2015.
Torquay-born Key initially joined the academy of his local club, but made the move to Exeter when the Gulls closed their youth set-up.
He had loan spells with Bideford Town and Tiverton Town, before being offered his first professional contract in the spring of 2018.
Key made his Grecians debut in November 2018 with a substitute appearance against Bristol Rovers in the EFL Trophy, and enjoyed two further outings in that competition the following season.
The 2020-21 campaign proved to be his breakthrough season as he made 48 appearances in all competitions, scoring his first senior goal in an EFL Trophy victory over Forest Green Rovers.
He made another 49 appearances the following season as Exeter finished second in League Two to secure promotion, and he remained an integral figure as the Grecians finished 14th in League One.