He enlisted in the Bundeswehr in 1966 as an officer cadet and graduated from Naval Academy Mürwik in 1968.
After that he served onboard Fast Attack Crafts and Destroyers. From 1974 he was trained as an antisubmarine warfare officer, and later undertook the Admiral staff course at the Bundeswehr Command and Staff College in Hamburg. In 1979 Feist became the commanding officer of the guided-missile Fast Attack Craft Greif.
From then on Feist served as Assistant Branch Chief, "Politico-Military Affairs" at the German Ministry of Defence in Bonn (1981–1983) and as Branch Chief "Planning" at the Allied Command Baltic Approaches (BALTAP) in Denmark (1984–1987).
He commanded the 2nd Fast Attack Craft Squadron based in Olpenitz between 1987 and 1990 and was instructor at the Bundeswehr Command and Staff College, which was followed by a service run at the Armed Forces Staff, Federal Ministry of Defence in Bonn as Branch Chief "Politico-Military Affairs". Further assignments led Feist to Supreme Headquarters Allied Powers in Europe in Belgium, the German Fleet Command in Glücksburg, and the Military District Command I, Kiel.
Feist was promoted to the rank of Vice Admiral in October 2000, when he became Vice Chief of Defence and Commissioner for Reserve Affairs in the Bundeswehr. Feist was promoted to the rank of Admiral (four stars) in 2002, thus becoming the highest-ranking officer in the Germany Navy, and he was appointed Deputy Supreme Allied Commander Europe (DSACEUR).
He held that position until 2004.
In addition, he was named Operation Commander for the European Union-led mission, Operation Concordia, to the Republic of Macedonia in February 2003. Feist was retired from active duty by Federal Minister for Defence, Doctor Peter Struck, on 15 September 2004. A Großer Zapfenstreich was held in recognition of his service.
Feist died in Timmendorfer Strand due to cancer.
Married Heidi Feist, February 27, 1970. Children: Torsten, Christian.