Karl-Heinz Knaup was born on May 23, 1950, in Sonthofen; he is the younger brother of singer Renate Knaup and the older brother of actor Herbert Knaup. From 1972 to 1975, he trained as an actor at the Zinner Studio in Munich. He then took on various theater engagements before making his on-screen debut in 1981 with a small role in the TV production "Jaipur Junction."

However, it was not until the late 1980s that Knaup appeared in additional film productions, such as supporting roles in Christian Wagner's "Wallers letzter Gang" ("Waller's Last Trip," 1988) and Jo Baier's "Wildfeuer" ("Wildfire,"1991), both times portraying a photographer. Most notably, from then on, Knaup appeared in both major and minor TV roles. In 1988, alongside Christopher Reeve and Donald Pleasence, he was part of the large ensemble cast in the U.S. production "The Great Escape II: The Untold Story". In the award-winning TV crime drama "Der Pakt - Wenn Kinder töten" (1995) with Daniel Brühl, he played the investigating commissioner.

In 1997, Knaup had a regular role as a senior fire officer in the 13-episode series "Die Feuerengel." He also played a recurring role in the six-part series "Zwei Männer am Herd" (1999).

Over the years, Knaup was frequently cast as an academic authority figure or dignitary: in the Hamburg "Tatort" episode "Der schwarze Skorpion" (2000), he played a colleague of a murdered professor; in "Der Ärgermacher - Wer hat Angst vor Jochen A." ("The Trouble Maker," 2002) and the biographical film "Margarete Steiff" ("Against all Odds", 2005), he played doctors; in the disaster film "Tsunami" (TV, 2004), he portrayed a legal advisor, in an episode of "Die Familienanwältin", a defense attorney, and in the feature film "Meine schöne Nachbarin" (2007), he played an artistic director. In the "Tatort" episode "Der Tod ist unser ganzes Leben" (2016), he portrayed a criminal superintendent, and in the TV crime drama "Das Tal der Mörder" (2018), he played a mayor.

Above all, Knaup took on various episodic roles in numerous TV series, such as "Polizeiruf 110", "Der Alte", "SOKO München", and "Die Rosenheim-Cops" - just to name a few. In addition, he regularly performed in theater productions until 2006, including at the Bad Hersfeld Festival, the Westphalian Chamber Plays, and the Komödie am Ku'Damm.

On the big screen, Karl-Heinz Knaup appeared only occasionally: in the fantasy film "Saphirblau" ("Sapphire Blue," 2013), he portrayed a grand master of magic, in the award-winning thriller "Trash Detective" (2015), he played the father of a suspected murder victim. He had smaller roles in the modern Heimatfilm "A Gschicht über d'Lieb" (2018) and the zany comedy "JGA - Jasmin. Gina. Anna." (2022). He played a lead role in "Ein stummer Hund will ich nicht sein" ("Always Say Boo to a Goose"), a documentary film with dramatized elements about the priest Korbinian Aigner, who was imprisoned by the Nazis in Dachau in 1941; Knaup portrayed Aigner in the dramatized scenes. The film was released in theaters in April 2025.