Millwall have agreed terms with Byron Webster on a two-year contract that will see the defender become a Lion on July 1.
The 27-year-old will complete his move to The Den once his current contract with Yeovil Town expires.
After helping Yeovil to promotion in 2012-13, he started 40 games and scored three goals from the back last season as Yeovil finished bottom of the Championship and were relegated back to League One.
Webster becomes Millwall's third capture of the summer following the arrivals of Carlos Edwards and Lee Gregory.