Johnson turned professional in late 2007 after a successful Walker Cup campaign and earned his 2008 PGA Tour card by finishing in a tie for 14th place at the 2007 qualifying school in December. He joined the winners circle towards the end of his rookie season by winning the Turning Stone Resort Championship in October 2008 and won again only four months later by claiming the AT&T Pebble Beach National Pro-Am. Johnson continued his affinity with Pebble Beach by making birdie at the final hole in 2010 to successfully defend his AT&T Pebble Beach National Pro-Am title defeating former world number one David Duval and two-time PGA Tour winner J. B. Holmes.
In 2011 he recorded his best finish in a Major Championship by finishing T2nd in the Open Championship at Royal St Georges, three shots behind Darren Clarke's winning total.Johnson is the first player since Tiger Woods to win at least once in each of his first six seasons coming out of college.