In recent seasons he has enjoyed loan spells with Rochdale, Morecambe and Lincoln.
Howe is expected to go straight into the Gillingham squad for their game with Colchester on Saturday.
Wayne Rooney has returned to Everton after 13 years at Manchester United.
Germany defender Antonio Rudiger has joined Chelsea from Roma on a five-year contract.
Wayne Rooney has returned to Everton after a record-breaking career at Manchester United.