The 21-year-old becomes boss Darren Way’s fifth January addition and bolsters Town’s attacking options for the remainder of the campaign.
Having spent the first half of the season on loan at Sky Bet League One outfit MK Dons, Seager links up with his hometown club for the first time in his career.
Manager Darren Way said: “It’s amazing recruiting a player born and bred in Yeovil.
“He knows the history of the club and was at Wembley in a Yeovil shirt in 2013.
“His committment to join us in League Two and leave MK Dons is massive and he’ll help us in our quest to climb the table.”
Snapped up by the Saints as a schoolboy, Seager was fast-tracked through the youth system before netting 20 goals in his maiden season with the Under-18s.
Completing his Academy graduation, Seager made his first team debut in 2015 – coming off the bench in an Emirates FA Cup tie against Crystal Palace.
Having turned pro in 2013, the highly-rated frontman signed a new four-year deal with the Hampshire outfit in 2015 fresh from netting 16 goals for the Under-21s and despite interest from Arsenal.
A loan spell at Crewe Alexandra two seasons ago was ended prematurely due to injury after a goalscoring start, before Seager netted three goals in 22 appearances for MK Dons up until the start of this month.