The move came five days after the Dolphins cut Johnson.
Miami needed a reinforcement because rookie running back Daniel Thomas hurt his hamstring Wednesday and sat out practice Thursday. He is day to day, coach Tony Sparano said.
Johnson originally joined the Dolphins on Aug. 23 and scored on a 22-yard run in their final exhibition game -- his first TD since 2008 with Kansas City. He sat out most of last season after his career was derailed by a series of off-the-field missteps.
Johnson practiced Thursday and said he was glad to get another shot at a comeback.
"I could have easily said I'm going to retire as a Chief," he said. "You knew coming back it was going to be a roller-coaster ride, and you expect that. You roll with the punches.
"I love playing and it's always going to be in me. I haven't lost that fire yet to be under the lights and to compete to be the best."
He may be under the lights as a backup to Reggie Bush on Monday, when Miami opens its season against New England.