The Bees pulled off something of a coup in securing the services of the former Fulham striker, but the 26-year-old has had to wait patiently for his debut.
However, the clearance has now been granted and John is eligible to play in Barnet's clash with Plymouth on Saturday.
Chairman Tony Kleanthous said: "I'd like to thank the fans for being so understanding and to my administration staff who have worked tirelessly over the past few weeks overcoming many obstacles in getting Collins' clearance."
Head coach Mark Robson added: "It's been an extremely long two weeks waiting for Collins' clearance and we are all relieved that another piece of the jigsaw is in place. Collins is an experienced player and we look forward to having him available."