Johnson was born in Columbia, South Carolina. He played collegiate golf at Coastal Carolina University. As an amateur, he won the Monroe Invitational and the Northeast Amateur in 2007 and played on the winning 2007 Walker Cup and Palmer Cup teams.
Johnson turned professional in 2007 and earned his 2008 PGA Tour card by finishing in a tie for 14th place in the 2007 qualifying school.
Johnson won his first PGA Tour event, the Turning Stone Resort Championship in October 2008. Four months later, he won his second event at the AT&T Pebble Beach National Pro-Am, a tournament that was shortened to 54 holes when the final round was cancelled due to strong winds and heavy rain, leaving Johnson the winner by 4 strokes over Mike Weir and six strokes over second round leader Retief Goosen, who shot a third round 2 over par 74.
