Trojan is set to almost double its workforce as it moves to a building at the old Visteon factory site in Fabian Way.
A total of 138 jobs will be created by Trojan Electronics, which began with a staff of four in Gorseinon in 2002.
The firm will invest £1m in the move but will receive £1.5m from the Welsh government to go towards turning the Kings Dock building into its new HQ.
The move is expected to be completed early in 2015.
Trojan, which employs 150 people, offers a repair and refurbishment service for products returned under warranty to major retailers.
It also runs multi-channel ecommerce platforms for blue chip companies and manufactures printed circuit boards.