Kačer graduated from the Ceramics School in Bechyně, where he also had his first experience participating in an acting ensemble. After completing the relevant exams and receiving his certificate (1955), he applied to study directing at the Theatre Faculty of the Academy of Performing Arts in Prague. He founded the Holubáři Theatre Ensemble under the Czechoslovak Union of Youth, which subsequently, in its entirety, received an offer for an engagement at the Petr Bezruč Theatre in Ostrava. Here Kačer was active as an actor and director from 1959 to 1964. He subsequently left to join a newly established theatre in Prague – The Drama Club (Činoherní klub), where he remained from 1964 to 1974. He later acted and directed at the State Theatre in Ostrava (1976–80), the E. F. Burian Theatre in Prague (1979–81), the National Theatre (1983–2015) and the Vinohrady Theatre (1986–90). He is currently with the Palmovka Theatre (Divadlo pod Palmovkou).

He has directed 70 theatre productions and has almost 160 roles to his credit. He has also been involved in many television and film productions. Kačer is married to the actress Nina Divíšková (*1936).