The player's current deal is set to run out in February, and his future at the club was in doubt prior to Gorman's appointment.
"Roger has still got things to learn, but he has really impressed me. He is the type of character I need," said Gorman.
Johnson, signed from Portsmouth by former Wycombe boss Lawrie Sanchez, has played the full ninety minutes in each of Gorman's first two games as Wycombe manager.
Meanwhile, Gorman has added a new face to the squad, bringing in 21-year-old winger Stephen Cooke from Aston Villa on a month's loan.