Keagy started out his career as a drummer, but over the years he has gained experience in many aspects of the music business. The day after Kelly graduated high school, he packed his bags and left home to pursue being a full-time drummer.

After years of playing the club circuit, he became the drummer for the San Francisco band Rubicon. Along with fellow members Jack Blades and Brad Gillis, he formed the band Night Ranger in 1979 as Stereo.

In 1989–1990, Jack Blades formed Damn Yankees (1989–1996, 1998) with Ted Nugent and Styx's Tommy Shaw, scoring a hit with the song "High Enough".In 1991, Night Ranger reformed with Gary Moon replacing Jack Blades on bass and lead vocals.

Then in 1996, the classic Night Ranger lineup of Jack Blades/Kelly Keagy/Brad Gillis/Jeff Watson/Alan Fitzgerald reunited. Fitzgerald departed in 2003, and Watson in 2007.