Thomke was born April 21, 1939 in Bienne/Biel Switzerland. The son of a physician, Thomke apprenticed as a mechanic at ETA in Grenchen and studied science at the Universities in Bern and Lausanne. After working at pharmaceutical firm Beecham, Thomke returned to ETA to help reorganize the company, which was under assault during the quartz crisis.
Thomke focused on consolidation of the industry and participated there during the merger with A. Schild. He became CEO of Ebauches SA in 1982 and joined the Board of Directors of parent company ASUAG. He was involved in the consolidation of ASUAG and SSIH into SMH under Nicolas G. Hayek, and was CEO of the consolidated company from 1984 through 1991.