Seitz was the older of two boys born to teachers Kerlin and Martha Seitz. The family moved several times, and while Karl Seitz spent most of his school years in Wisconsin, his senior year of high school was spent in Troy, Alabama, where he was recognized as the graduating senior with the highest grades in math in 1961. Upon graduation Seitz joined the U.S. Naval Reserve, serving three years, primarily aboard the USS Caliente, a fleet oiler.
After his release from active duty, Seitz moved to Birmingham in July 1964 to attend Birmingham-Southern College, where he enrolled that fall. That Christmas, he took a temporary job as a sales clerk at Pizitz. In 1965, he was forced to briefly drop out of college due to financial difficulties, but after taking a job at the Jack Cole Trucking Company, first as a manifest clerk and later as a billing clerk, he was able to resume his studies at Birmingham-Southern later that year.
Seitz worked full time at Jack Cole until it was bought out by another trucking company and he was laid off in August 1967. He started his next job at the copy desk of the Birmingham Post-Herald on September 11, 1967. Working full time at the Post-Herald, he graduated with a B.A. in political science in the summer of 1969.
While Seitz was at Birmingham-Southern, he met fellow student Pat Floyd. The two were married in 1970 and had their only child, a son named Lee, the following year. The family moved from Birmingham to Homewood in 1974.
Seitz continued his job at the Post-Herald after getting his degree, working his way up. In 1970 he became the assistant news editor. He was promoted to chief editorial writer in 1972 and wrote a regular column through the 1970s. The chief editorial writer position evolved into editorial page editor by 1978. As he moved into a more senior position, Seitz's opinions appeared less often under his own byline, but continued to be reflected in the unsigned editorials of the Post-Herald's "Our Views" section, a name Seitz decided on to contrast with the letters to the editor section named "Your Views."
As a senior member of the newspaper, Seitz had several important jobs beyond creating the editorial page each day. He also helped negotiate labor contracts with the unions, was on the board of the Goodfellows Fund, and sometimes filled in for the paper's editor when he was away.
Seitz was also a member of the 1986 Leadership Birmingham class. He participated in Birminghan-Southern College's Executives in Residence program in 1987. In the early-to-mid 1990s he also became a semi-regular guest on Alabama Public Television's For the Record news show, appearing as one of the guest journalists on Fridays every few months through 2005.
Seitz was still editorial page editor when the Post-Herald published its final edition on September 23, 2005, after which he retired. In his final editorial, he wrote, "for more than 30 years, it has been my pleasure – most of the time – to chose the items that appear on this and the facing pages and to write many of the editorials that have angered and pleased the people who are their subjects and readers." He has since had some freelance writing accepted by Everton's Genealogical Helper, is working on some science fiction stories, and continues his genealogical studies.
- "Atkinson Now Writing Column in Birmingham." (November 1970). Scripps-Howard News, vol. 25, no. 2.
- Seitz, Karl. (September 23, 2005). "It's been a pleasure – most of the time." Birmingham Post-Herald.
- Seitz, Karl. (c. July 5, 2007). Personal communication.
- USS Caliente AO-53 Crew List S-Z. (n.d.). USS Caliente AO-53 Association. Accessed March 13, 2008.
- Seitz Site, Karl Seitz's personal web site