Millwall sign Bradford City left-back James Meredith on a two-year contract, to start on 1 July.
Millwall release goalkeeper David Forde and full-back Joe Martin following their promotion to the Championship.
The EFL says a pitch invasion by Millwall fans after their play-off final win at Wembley was "completely unacceptable".
Millwall sign striker Tom Elliott from League One club AFC Wimbledon on a two-year contract.
Millwall midfielder Shaun Williams signs a one-year contract extension with the newly-promoted Championship club.