Greg K. is one of the founding members of The Offspring alongside singer Dexter Holland. Prior to forming The Offspring, he was also on the track and field team at Pacifica High School in Garden Grove, California, along with bandmate Holland, and was also in the Math Club. Greg K. and Holland had been playing locally since the early 1980s and formed Manic Subsidal in 1984. After hiring Noodles as their new guitarist, Manic Subsidal changed their name to The Offspring in 1986.
On May 28, 2008, Greg K. announced on The Offspring's website that he was taking a hiatus from touring because of a "scheduled family matter" but would be returning to the fold by mid-June. Face to Face bassist Scott Shiflett filled in for him on those shows. The "scheduled family matter" turned out to be a new child, as he became a father for the fourth time.