Born in Gross-Fahlenwerder, Grünberg served in the Luftwaffe of Nazi Germany. Following flight training, he was posted to Jagdgeschwader 3 "Udet" (JG 3—3rd Fighter Wing) in 1942, operating on the Eastern Front. He claimed his first aerial victory on 19 August 1942. On 9 May 1944, Grünberg was appointed Staffelkapitän (squadron leader) of 5. Staffel (5th squadron) of JG 3 and was awarded the Knight's Cross of the Iron Cross on 9 June 1944. In January 1945, Grünberg was posted to Jagdgeschwader 7 "Nowotny" (JG 7—7th Fighter Wing), the first jet fighter wing where he served as a Staffelkapitän of 1. Staffel. He died on 16 January 1998 in Ellerau.
