His Tigers' career comes to a close with 30 goals to his name from 78 appearances in all competitions, the last of those ironically being played against Orient 9 days ago.
O's manager Paul Brush described the forward as an "ideal signing."
Brush said: "He's a London lad who's coming back to his area with a determination to succeed and prove Peter Taylor wrong over him.
"He wants to play for us and he's an ideal signing at this stage of the season. It's no secret that we haven't scored enough goals this year, and Gary's a goalscorer who has a presence about him and if he hits form we know that there will be a lot left for us to play for this year."
Meanwhile, it is unclear as to whether or not Lawrie Dudfield will also be on the move.