Ranger was suspended by the League One club on 12 January after a "breach of discipline", and was stopped from playing until the inquiry was over.
Following an FA disciplinary hearing on Thursday the 25-year-old is now eligible to play again, 28 days after the initial club suspension.
He could face Millwall on Saturday, with the Shrimpers sixth in the table.
Early in January, Ranger admitted an online banking fraud, but the suspension is believed to be unrelated.
Southend United striker Nile Ranger is available for selection again following a Football Association investigation.