Third-generation racer Seton joins team owner Jason Gomersall in the entry, which is backed by the latter’s iSeek company.
Seton drove for the Gomersall squad in the Super2 Series before stepping back to a largely off-track role with the team in 2024.
The iSeek entry adds to the Miedecke Motorsport Mustang that debuted in the category at the start of the season.
Gomersall Motorsport runs three cars, with a BMW M4 GT4 F82 and Mercedes-AMG GT4 also among its line-up.
Round 5 at Sydney Motorsport Park has drawn a season-high field, which can be viewed here.
Practice begins today, with qualifying this evening. Saturday and Sunday will each see the GT4 field compete in a 60-minute race.