Karl is a native of Hamilton County. He graduated from Carmel High School in 1974, from Ball State University (magna cum laude) in 1979, and from Indiana University School of Law - Indianapolis (now McKinney School of Law) in 1983. Karl was admitted to the bar and began his practice in 1983. He has been a contractual public defender in Hamilton County Courts since the 1980s and currently maintains public defense contracts in Hamilton County Superior Courts No. 1 and No. 3 while representing private clients as well.