The defender, who helped the Grecians achieve back-to-back promotions from the Conference to League One between 2007 and 2009, has been without a club since leaving Scottish Premier League side Hamilton Academicals in the summer.
The 30-year-old Barnstaple-born player is a popular figure with the St James Park faifthul as he is a product of the club’s youth academy and went on to captain the side in one of their finest moments as they achieved promotion back to the Football League in 2008 with a Conference play-off final victory over Cambridge United.
Seaborne can play centre-half or left back and his return to his boyhood club comes at a crucial time with Troy Brown and Luke Croll both currently out injured.
Speaking about his return, manager Paul Tisdale said: “We are pleased to welcome Danny back to St James Park. He was a popular figure in his previous spell at the club, having graduated from the club’s youth academy and helped us to achieve back-to-back promotions.
“He will strengthen the competition for places we have in defence, which has been hit recently due to the injuries to Troy Brown and Luke Croll, and offer a wealth of experience having played in the Championship and Scottish Premier League since departing St James Park in 2010.”